September 22, 2025 • 44 mins
Why do people on a date speak in innuendo? Why do dictators squelch protests? Why do humans stand apart from the rest of the animal kingdom by blushing, laughing, and crying? And what does any of this have to do with bullies, George Costanza, or cancel culture? Join this week with cognitive scientist Steven Pinker as we discuss his new book on common knowledge: “When Everyone Knows That Everyone Knows”.
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Speaker 1 (00:05):
Why do people speak in innuendo when they're on a date.
Why do dictators try to squelch protests, Why do we
join up with bullies to gang up on an outcast.
Why do humans stand out from the rest of the
animal kingdom by blushing and laughing and crying? And what
(00:25):
does any of this have to do with George Costanza
or when Harry met Sally, or anonymity on social media
or cancel culture, or why we generally don't say everything
we mean. Welcome to Intercosmos with me David Eagleman. I'm
(00:45):
a neuroscientist and author at Stanford and in these episodes
we sail deeply into our three pound universe to understand
why and how our lives looks the way they do.
(01:13):
Today's episode is about a phenomenon known as common knowledge,
which is something that I know and you know, and
we both know that we know it. Now, this could
seem like a very particular sort of thing to pay
attention to, but many psychologists and economists over the past
decades have started to think that a deeper understanding of
(01:35):
common knowledge could explain all kinds of things about human
nature and behavior and societies, and for a very long time.
This has grabbed the attention of my friend and colleague
Stephen Pinker, who just this week has a new book
coming out on common knowledge called When Everyone Knows That
Everyone Knows, And so I called him up to discuss
(01:57):
this topic. I'll take just a moment to frame this
before I begin the interview. At the heart of the
issue is that we are a massively social species. We
form lifelong relationships, and we join clubs, and we're parts
of tribes, and we're citizens of countries. And we're also
a highly intelligent species, and we spend a lot of
(02:18):
our time, usually unconsciously, figuring out who knows what and
what we know in common, and for that matter, thinking
about how we can expand common knowledge with the right signals,
and often how we could hide things from becoming common knowledge.
The key thing to understand for today's conversation is that
(02:39):
common knowledge is not just about a bunch of individuals
each knowing something. It's that each person knows it and
knows that everyone else knows it, and knows that everyone
else knows that they know it, and so on. And
the argument is that it's this ladder of shared awareness
that allows societies to coordinate. Think about something like the
(03:00):
game of chicken, where two drivers speed towards each other.
Each knows the situation, but the critical factor is whether
both drivers know what the other is willing to do,
and whether both know that the other knows. And the
effects of common knowledge stretch from two people all the
way up to countries. For example, history is filled with
(03:22):
moments when private thoughts turned into common knowledge and changed
the world. So, for example, in nineteen eighty nine, East
Germans had long doubted the regime, but it was only
when tens of thousands gathered in the streets when everyone
could see that everyone else had the same doubts. That's
when the Berlin Wall fell. Stock Market bubbles and crashes
(03:45):
run on the same sort of principle. Investors don't care
only about the value of a stock, but about what
everyone else believes everyone else believes about its value. So
this is the type of thing that Pinker's book explores,
all all the ways in which common knowledge permeates everyday life.
(04:06):
Common knowledge, for example, is why etiquette works. You don't
just know the rules, you know that others know them too.
It's why red lights function not because you fear the police,
but because you know that everyone else knows the rule
and is going to stop. It's why children learn to
play Peek a boo, because the delight comes from that
shared loop of I know that, you know that I'm here.
(04:29):
So today we'll explore the phenomenon of common knowledge. Stephen
Pinker is a cognitive scientist and linguist at Harvard and
he's a longtime bestselling author who is famous for illuminating
the hidden structures of human thought and society. His new
book dives into the puzzle of common knowledge, how it arises,
why it matters, and what it reveals about the architecture
(04:52):
of our social minds. Stephen joins me, Now, so, Steve,
we are an intensely social species and there's a lot
that has to happen in order to get us to
coordinate as a result. And this is the thing you've
been thinking about, So tell us how do we coordinate
(05:13):
as a species.
Speaker 2 (05:14):
Well, any two agents who need to coordinate need common knowledge.
The theme of the book, common knowledge, being the state
where I know something, you know it, I know that
you know it, you know that I know it, I
know that you know that I know that you know it,
ad infinitum. Why Because it isn't enough for each party
to know what the other one is going to do,
(05:36):
because the other party guessing what the first one is
going to do may do something complete different. So just
be concrete. If we're going to rendezvous and we don't
generate common knowledge by a conversationalist, and my cell phone
goes dead, so each of us asked to guess where
the other one is going to go. It's not enough
for me to know that you like to go to Starbucks,
because you may know that I like to go to Pete's.
(05:58):
And so if I go to Starbucks, that's where you're
going to go. You might go to pizza because you
think that's where I'm going to go. And well, I
know that, okay, so I'll go to Pietz because Dave
knows that I like to go to pizza. But wait
a sec Dave knows that I know they likes to
go to Starbucks, so he's going to go to Starbucks
after all, and so on. Nothing short of actually blurting
it out in each other's presence will get you on
(06:18):
the same page. Some kind of public perceptible self evidence signal.
That's what is needed for coordination.
Speaker 1 (06:27):
You've, of course spent much of your career studying language,
and so you see language as one way of establishing
that common knowledge give us a sense of that, Yeah,
you know that.
Speaker 2 (06:39):
I'm trying to get you to believe something because you
know that I'm saying something with the intent that you
believe it. That's kind of what language is. So it's
a common knowledge generator when it is something is blurted out.
What got me interested in this whole topic is actually
almost the converse cases in which we try to avoid
(07:00):
common knowledge when we don't say something in so many words,
but we put our meaning between the lines. We count
on our reader to connect the dots. We use euphemism
or innuendo or hinting or beating around the bush or
hilly shallowing, which is a lot of language. That's one
of the reasons it took so long to get computers
to understand language. If you simply parse who did what
(07:22):
to whom based on the subject of the verb and
the object, you're really not going to understand what people
actually meant, such as if you could pass a salt,
that would be awesome. Okay, now think about that. I mean,
that doesn't make it much sense. It would literally be awesome,
And you know, it's not like you're just pondering possible worlds.
That's not the meaning. Everyone knows what the meaning is.
(07:43):
It's give me the salt, and a lot of languages
like that, and linguists have long known it. But the
question is why what do we try to accomplish when
we avoid blurting something what we want out? In so
many words, what I suggest is that the we're avoiding
common knowledge. That is, each one knows what the other
one is doing, but you may not know that the
(08:04):
other one knows that you know that they know, and
that allows you to preserve a certain relationship, relationships being
coordination problems, as we mentioned at the top of the conversation,
a relationship like being friends, being lovers, being a supervisor
in supervisory, being transaction partners. Those are all matters of
common knowledge. We're friends not because we signed a contract,
(08:26):
but because each one knows that the other one knows
that there we're friends, and that can be threatened by
certain things that could become a common knowledge that contradict
the basis of the friendship, like a sexual proposition. So
why do people say things like I want to come
up for Netflix and show, or you want to come
up for coffee when you know, though you know, let's
(08:48):
say it's a man saying it to a woman. You know,
she wasn't born yesterday. She's a grown up, she knows
what it means. But it's still way better than Hey,
you want to come up and have sex, which would
be you know, both parties. You are pretty uncomfortable, even
though would you like to come up for coffee? Doesn't
make them uncomfortable? How come that was the problem that
I took up in a previous book, The Stuff of Thought.
(09:10):
Language is a Window into human nature, which had a
chapter called games People play on language as a window
into social relationships and in trying to figure out why
we don't just blurt out what we mean. Other examples
being say a failed bribe. Let's see you trying to
jump the queue in a restaurant and you slip the
(09:30):
major DA twenty dollars bill and say, I just wondering
if you might have a cancelation, or this is an
important night from you. Is there any way to shorten
my weight? Why don't people just say if I give
you twenty dollars, will you see me? Right? Away or fundraising.
I've seen this a lot at Harvard. I'm sure you've
seen a similar thing where the dean will say to
(09:50):
the rich people in the audience, we're counting on you
to show leadership, to be a friend to the university
instead of the reason we're all here is you're going
to open your checkbook and write, you know, a check
for five million dollars. That's another case where people don't
say what they mean. Why not? And here's the answer
that got me interested in common knowledge. And I've done
(10:13):
studies to back this up that if it's do you
want to come up for coffee? Well, you know, she
knows what he means, and you know obviously he knows
what he means. But does she know that he knows
that she knows? With an innuendo like would you like
to come up for coffee, she could think, well, maybe
he thinks I'm naive, and if I said no, maybe
(10:34):
he thinks, you know, caffeine would keep me up. Even
though she knows that she's turned down a sexual overture,
he knows it as well, but he could not know
why because she knows that he knows. And likewise he
could think, well, you know, maybe she thinks I'm dead,
Maybe she thinks that I think that she's just turned
down coffee. Uh. They can maintain their platonic friendship with
(10:55):
the common knowledge that it's just about companionship. Whereas he
said you want to come up for half sex and
she said no, they can never be platonic friends in
the same way. Again, the intuition is it's out there,
you can't take it back, And I suggest that technically
what's happening is that the blurted out speech generates common knowledge.
(11:18):
Common knowledge is the basis of our relationships. Their coordination, games,
euphemism and innuendo get a message across without generating common knowledge,
and that's why we fall back on it so often.
Speaker 1 (11:30):
Okay, so that's how we sometimes try to mask common knowledge.
Tell us about how common knowledge is useful in society,
society wide, let's say, with public demonstrations and politics and economics.
Speaker 2 (11:44):
Yeah, a lot of our large scale coordination, not just
two friends or Roande going for coffee or agreeing to
be platonic friends, but large scale things like everyone recognizing money,
Like why do I accept a green piece of paper
in exchange for something of value? Well, because I know
that other people will accept it and give me something
(12:07):
of value. Why would they do that, Well, they know
that still other people would accept it. So the value
of currency depends on common knowledge. Everyone knows it's worth something,
and that's what makes it worth something. The fact that
everyone knows that everyone knows it. A lot of power
depends on common knowledge. There are laws, there's courts, there's
a police force, there's a jail. But most of the
(12:28):
time people just follow the law, even though big brothers
watching them twenty four to seven. However, these things can change.
It's not easy to change them when the basis of
power or money is just common knowledge, because everyone has
an interest in keeping up the common assumption. But sometimes
(12:48):
it can unravel. In the case of power, if there
is a public protest, everyone shows up at a public
square at the same time, the same place, everyone sees
everyone else there. Previously, maybe that everyone was resentful of
the system, thought it was inefficient and oppressive. They may
even have suspected that everyone else had the same feeling,
(13:11):
but they didn't know that other people knew that. They
knew they couldn't coordinate by all rising at the same time,
and so the regime could keep them in their place
by preventing common knowledge. And that's why dictators don't allow
freedom of assembly, freedom of the press, freedom of speech,
precisely because they're afraid that people coordinating which they could
(13:34):
only do with common knowledge, could acting together overpower a regime. Likewise,
in the case of going back to money again, if
the value of money depends on common knowledge, then when
the common knowledge is threatened, the value of money can disappear.
And that's what happens when you get hyperinflation, people taking
home their wages in a wheelbarrow because no one will
(13:55):
accept it anymore, or a bank run where people withdraw
their savings, not necessarily because they think that there's anything
wrong with a bank, but as long as there's a
rumor that other people think that there's a problem with
the bank, and they're withdrawing their money out of fear
that still other people will withdraw their money, it suddenly
becomes rational to withdraw your money while the bank still
(14:17):
has money to withdraw. And that can cause a bank
to fail, that can cause the whole economy to fail.
That's what happened in nineteen twenty nine. And so when
Roosevelt said the only thing we have to fear is
fear itself. He was stating a theorem of common knowledge
that was quite literally true, that what people had to
fear was fear itself, and the fear of fear, the
recursive fear, the common knowledge, could actually change the value
(14:41):
of those financial institutions.
Speaker 1 (14:45):
So here's something I wanted to dig in with you
about after reading your book. How do we think about
false common knowledge? By which I mean, let's imagine that
you and I engage in a public protest and we
look around and we see a thousand people around us.
We say, look, everybody clear feels this way, but we're
not aware of that across town there's a larger protest
with ten thousand people in it, and we have the
(15:07):
impression that everyone feels the same way we do about something.
Speaker 2 (15:10):
I mean that technically be common belief rather than common knowledge,
But different pools of people can have different common beliefs,
and there can also be common misconceptions where prior to
the protest, there are cases where people think that everyone
else believes something. In fact, everyone could believe that everyone
else believes someone something and no one actually believes it,
(15:33):
sometimes called a pluralistic ignorance. Or a spiral of silence.
Speaker 1 (15:37):
What's an example of that.
Speaker 2 (15:39):
A classic case study of pluralistic ignorance in social psychology
was when some psychologists interviewed the guys in the fraternity.
They found that every one of them thought that it
was really stupid to drink so much that you pass out,
but everyone thought that all the other frat bros thought
it was cool. No one actually thought it was cool,
(15:59):
but that all the others thought it was cool. And
there are probably a lot of cases like that. I mean,
an extreme case would be The Emperor's New Clothes, where
everyone thought that everyone else thought that who were seeing clothes,
no one actually saw clothes, And it took the little
boy blurting it out generating common knowledge, for the common
(16:19):
misconception to flip into common knowledge. The Emperor's New Clothes
is a story about common knowledge. The boy wasn't telling
anyone anything they didn't already know, but it was changing
the state of their knowledge because now everyone knew that
everyone else knew, and that changed their relationship with the
Emperor from a deference to scorn and ridicule.
Speaker 1 (16:59):
I do worry a little bit, though, about people assuming
politically common knowledge and saying, Hey, if I just make
some innuendo, everyone will understand what I mean by this,
because that often doesn't work, especially now.
Speaker 2 (17:14):
Well, the thing about innuendo is that it has to
be calibrated so that it is recognized by a kind
of willing recipient, but can be denied by an unwilling recipient.
So it has to be calibrated in that zone, and
there can be errors in either direction. Where there's an
(17:35):
episode of Seinfeld where George Costanza is invited up for
coffee and says no because he's got to get to
work early the next morning, and then as he's walking out,
he says, oh, my god, coffee doesn't mean coffee. Coffee
in sex. So there's the Costanza problem that it could
be so subtle that it goes over the head, or
(17:56):
there could be conversely, it's so blatant that the the
unwilling hearer calls you on it again. You know, all
of these things, by the way, are worked out in fiction,
in comedies, comedies of manners, situation comedies. They kind of
allow us to exercise our facility for recursive mentalizing, that is,
(18:19):
getting inside the head of other people, getting inside the
head of other people and so they're often worked out
that so often were drives fictional plots. But the opposite
is when when Harry met Sally, and Harry, you know,
early on, is kind of complimenting Sally and they just
met kind of a little too insistently, and then she
(18:39):
blows the listle. She says, you're coming on to me,
which leads to a wonderful discussion of common knowledge. I mean,
not not in those words where he says, okay, let's
say I was coming on to you. What are we
going to do? I take it back? Okay, I take
it back, and she says, you can't take it back.
He says, what do you mean you can't take it back?
You know, what are we going to do? Call the
(18:59):
cop and she says, it's out there. It's too late,
So it's out there. That is a metaphor for common knowledge.
That is something that's out there, is something that you
see other people see, you see them see it. And
direct speech or even in this case, indirect speech that
was not indirect enough. It kind of exceeded that. The
(19:22):
cutoff is out there, and when it's out there, it
changes the nature of the relationship. They were no longer
just near strangers, platonic friends. He had turned it into
a sexual relationship, which you rebuffed.
Speaker 1 (19:37):
Great, So I want to return for just a second
to literature, which you mentioned fictions, because I made the
argument on this podcast little while ago that I'm not
so worried about AI completely taking the job of writers.
And I listened five different reasons, but one of them
had to do with the fact that we could all
(19:57):
generate totally bespoke literature, just like Kings of Yesteryear would do.
But we lose something there, which is that a big
part of literature is the social glue, the fact that
everyone else has read the same story. I don't want
my Game of Thrones to have a different outcome than
your Game of Thrones. So my question to you is,
what is the reason we desire common knowledge so much?
Speaker 2 (20:20):
I think it's a great example, and people may not
remember that back in the nineties, when the internet first
became a thing, there was the idea that you could
dial in whatever ending to a story you wanted. That
fiction would be, movies would be the same. Everyone could
watch that movie. Maybe let's they didn't take off. And
I think it's the reason that you identified, namely part
(20:43):
of the experience of art is that it's common knowledge.
You know about something at the same time you know
that everyone else knows about it, and that's what gives
you something in common that can reinforce a social relationship.
With friendship, a movie with friends, you talk about it
with friends, and the common experience is one of those
(21:05):
things that kind of go makes friends friends. They go
through things together, they share common interests. The basis, the
common knowledge, that's the tacit basis of friendship is that
we're kind of there's a kind of a mind mild,
even a you know, a body meld, where that we
(21:25):
are in physical proximity, We hug, we shake hands, all
the more intense and romantic relationship.
Speaker 1 (21:31):
Okay, So I want to return and dig in just
a little on this point because I'm fascinated by this
about false common knowledge what I'm calling that or a
misconception about it. So, for example, recently, Charlie Kirk was
assassinated in broad daylight, and if you look on X
and if you look on blue Sky, you find very
(21:53):
different stories about that. And presumably the people who are
tweeting or blue skying are thinking, hey, this is great.
We have shared common knowledge. But you in fact have
two groups of people. I'm exaggerating a little bit the difference,
but you have different groups that have beliefs that they
believe are shared by everybody. Just one second example. This
(22:17):
My grandmother I remember many years ago in Florida said
I can't believe that so and so just one governor,
because I don't know anybody that voted for him. And
it was true, of course she didn't know anybody, but
it doesn't mean that the majority of the state didn't
vote for him.
Speaker 2 (22:33):
Nonetheless, Yeah, I mean common knowledge, or more accurately, in
a lot of these cases, is common belief, That is,
you believe something, you believe that other people believe that
you believe it, and so on. Is relative to a network,
a community which can be disconnected from another network, and
the common knowledge is often generated since none of us
experience everything firsthand. In fact, on for politics, we experience
(22:56):
almost nothing firsthand, and we read about it, we hear
about it. If the sources are disjoint, then the pools
of common knowledge within each of these networks could be disjoined.
And that happens partly from social media, as even feeds
within a platform, but even more so when they're different
platforms like X versus Blue Sky, or in the case
(23:17):
of cable news, do you watch Fox News or do
you watch CNN or do you watch MSNBC. So one
of the users I take up in the book, and
this intersects with my interest in academic freedom and freedom
of speech in another part of my life where I
co founded and I'm the co president of the Council
and Academic Freedom at Harvard. Why is free speech so
(23:40):
important and all the more so in a country? Why
is freedom of speech enshrined in the First Amendment to
the American Constitution, Freedom of the press, freedom of assembly.
So what is it about speech that can be so
threatening to a dictator? You might think, Well, the dictator
would be tend to let people bitch and moan all
(24:01):
they want. He's what with the guns, And as Mao said,
power comes out of the barrel of a gun. So
why should a public protest or a critical editorial be
so threatening to a dictator? Well, the reason is, as
Gandhi said in the eponymous movie, he says to a
(24:26):
British officer in the end, you will leave because there's
simply no way that one hundred thousand Englishmen can control
three hundred and fifteen million Indians if the Indians refuse
to cooperate. So that's just a truth about numbers then,
But it raises the question, how do you get three
hundred and fifteen million people cooperating or in this case coordinating. Well,
some public event demonstration where you're protesting, you can see
(24:52):
everyone else protesting, and everyone can see everyone else. You know,
the time is now a prominent public uh declaration you know,
Jacques or an article. Everyone knows now that it's public
that everyone hates the regime and people can, you know,
either storm the palace or just refuse to work or
(25:15):
to cooperate. And so dictators don't want that to happen.
They want to prevent the generation of common knowledge, which
is why police states control both public assembly and public media.
I give a joke. I recount a joke from the
era of the Soviet Union in which a man is
handing out leaflets in Red Square and of course they're
(25:35):
sure enough the KGB arrested. They take them back to headquarters,
only to discover that these leaflets are blank sheets of paper,
and they think, what is the meaning of this? And
he says, what's there to say, it's so obvious. So
that's a joke about common knowledge. Namely, he was being
subversive because by the very act just handing out leaflets
didn't matter what they said. That now everyone who accepted
(25:58):
the leaflets accepting seeing everyone else except the belief that
they all knew that there was something to protest, and
they didn't have to be told what it was because
they knew privately what it was. The act of communication
was that giving it out in a public square made
the private knowledge common, and that was threatening to the regime,
which is why, in a case of life imitating a joke,
(26:22):
Putin's regime has arrested people for carrying blank science.
Speaker 1 (26:28):
I'm sorry to return to this point, but if you
stood on a street corner and said I'm protesting, and
you handed out blank sheets of paper, the lefties would
think one thing from the blank sheet, and the right's
would think another thing. And so in an ideal sitution,
I mean, we look at the Soviet regime as a failure,
and so we say, okay, it was obvious what he
(26:49):
meant by that. But I'm interested in the fact that
we each have very different internal models. Let's say, with
politics and so the transmission of common knowledge isn't so
easy in a sense.
Speaker 2 (27:03):
Well, yes, I mean it depends on a conspicuous public
signal and in general from a trusted source and who
trusts who can vary between interconnected but disjoint networks of people.
But it's not, you know, it's not the case that
everyone goes that own way. Otherwise we wouldn't have society,
(27:24):
we wouldn't have science, we wouldn't have markets, we wouldn't
have currency.
Speaker 1 (27:28):
But we do have parties. We do have two different
parties that increasingly disagree more and more we do.
Speaker 2 (27:34):
Yes, I mean that, As I said, there can be
the common belief within semi disconnected networks, within each of
which you have common belief, but not necessarily in the
the entire group. The general phenomena are that common knowledge
is generated by public signals that people see when they
(27:58):
know that everyone else sees sees themselves seeing it. And
again that can be relative to pop the population and
the connected network that sees each other seeing something at
the same time.
Speaker 1 (28:12):
So tell us about cancel culture and also why cancel
culture is more possible in a world where people can
hide behind keyboards.
Speaker 2 (28:20):
Yes, I have a chapter in the book called the
Canceling Instinct, and it does touch on my interest in
academic freedom, but the point of the chapter isn't so
much to make the case for academic freedom, though I
do reprise that, but as a psychologist, to ask, why
is there an urge to censor, to cancel, to punish
(28:40):
people for their opinions. Now, of course that's been true
for all of human history, or heretics have been burned
at the stake or crucified. But you think that in
universities of all places, for the arena where we ought
to be, not treat beliefs as sinful. May be mistaken,
(29:01):
maybe illogical, but then you point it out, why do
you try to destroy the person who's ventured that opinion.
That's the phenomenon of cancel culture, and I suggest it's
because a combination of two psychological phenomena. One of them
is that even though the whole basis of science and
(29:23):
scholarship is there is a truth, we have means to
try to approach it. We may be mistaken, but we're
not bad people because we're mistaken. That you believe things
to the extent that there's good evidence for, good arguments
for it, that whole complex of beliefs is kind of
weird in human history. And the more common attitude is
(29:49):
for most people most of the time, is your beliefs
are a reflection of who you are, whether in particular
what tribe you belong to, and whether you're a good person,
who usually means upholding the sacred beliefs of your tribe.
Now that is poison for science and for scholarship and
for academia. But it is the way that people think
(30:11):
that the beliefs I mean putting aside beliefs about here
and now, I mean there are you know, people don't hallucinate.
They know, you know there's food in the fridge. There
isn't food in the fridge. But when it comes to
more bigger questions, where did humans come from? Why is
their disease? Why are their revolutions? Why is their wealth
(30:34):
and inequality? Things that we academics tend to think can
be answered by the methods of science and scholarship. But
most people is what you believe signals what tribe, what
coalition you belong to, And you're bad if you have
the wrong belief So if you have that kind of
(30:54):
built in flaw in human belief, then there can be
norms as to what you believe in what you don't believe.
And norms are matters of common knowledge. They exist because
people believe they exist. They can be threatened if people
flout them and get away with it. So and we
(31:29):
have everyday social norms. You don't go around naked, you
don't make you pass gas in public, you don't tell
ethnic jokes anymore, you don't insult people's appearance to their face.
All these norms are held up just because it isn't done,
and everyone knows that it isn't done. Conversely, if it
is done, the norm can unravel. So people often feel
(31:53):
the need to prop up norms by if noting when
they're flouted in public and then punishing the violator in public.
And the punishment has to be public for it to
prop up the norm, which is why we used to
have public hangings and pillories and stocks and crucifixions. Only
(32:15):
if you have everyone seeing that the person is punished,
could the norm survive well. I think we now have
an equivalent, often an electronic equivalent, in social media, where
if someone does flow a norm, that is, they express
an opinion that goes against what you take to be
the moral convictions of your tribe. People feel the urge
(32:37):
to punish it in public, and that's really easy to
do on social.
Speaker 1 (32:41):
Media and the anonymity of being behind the keyboard. I think,
you know, it's just like the trolley dilemma, where if
you have to push the person with your hands, it's different.
You activate these motional networks and you're less likely to
do that. But if you have to pull the lever
so that only one person gets killed instead of five people,
(33:01):
then most people are perfectly willing to do that at
a distance. And it strikes me it's the same thing
with the anonymity.
Speaker 2 (33:07):
Well, that's right. And it also and this does relate
to another common knowledge phenomenon, that is that our social relationships.
Are we friends? Are we lovers? Are we boss and subordinate?
Are we neighbors, members of a civil society? A lot
(33:28):
of these are reinforced by common knowledge generators. Eye contact, handshakes, laughter, blushing,
eye contact, things that can't be denied. That is, you
look someone in the eye, you're looking at the part
of them that's looking at the part of you that's
looking at the part of them that's looking at the
(33:48):
part of you, ad infinitum. So it's an eye contact
is a common knowledge generator, and the common knowledge that
these signals generate tend to be things like, well, we're
all acting like we're members of a community. So indeed,
when those signals are present because you're face to face,
(34:09):
then that can restore the norms of how you deal
with a person in a peer group, namely, you don't
insult them to your face. Without those common knowledge generators,
such as in the anonymity of a keyboard, then you
can insult people, you can denigrate them, you can try
to destroy the reputations in a way that would be
kind of unthinkable in a face to face situation.
Speaker 1 (34:31):
There's one piece I want to return to about cancel culture,
which is why everybody jumps on the bandwagon. You had
a section in your book about moral condemnation and why
it's better to join the bullies than to take the
risk of being bullied.
Speaker 2 (34:46):
Yeah, yeah, give us a sense exactly. I mean, it's
a kind of a playground dynamic that many of us
remember sometimes with shame, when we may have joined the
bullying mob and out of fear of becoming the kid
that everyone picks on and there is there's an equivalent
in academias. I had to say where I mean, it
(35:07):
has no place because we're all in it together trying
to find the truth. But you get the instant petition
with six hundred signatures, which can usually gin up on
social media. There are enough grad students in the country
that you can get get this is to sign some
condemnatory petition. But I think it is some of the
same dynamic, and there is a dynamics. Sorry to keep
(35:30):
relating things to common knowledge, because it is the theme
of the book, the theme of our conversation, but I
do think that it governs many human interactions. There's a
theory from a former post doc online Peter to Sholey
and his former advisor Rob Kurzband that we know no
one is an island. We really want to be part
of some group, some posse, some band of brothers, because
(35:54):
you know we're sitting ducks. If we're isolated, how do
you know which group to join? You don't want to
be on the losing side. If you can find some
sin that someone has committed and you all jointly recognize
that they are a sinner, they've broken some norm some law,
you gang up on them. That's a and it's common
(36:16):
knowledge as you know that the other people recognize that
same violation. It is a basis for forming a coalition,
and people often will band together and to single out
some victim as and there's something that feels right about
being in that band, and it is the basis that
the coalitions could form and the target suffers their kind
(36:38):
of collateral damage. Probably the episode from fiction that kind
of draws that out of the most is the famous
story by Shirley Jackson called The Lottery, came out in
the late forties, often assigned in high school and debated
ever since, where the town folk of a Bucolic village
every year choose someone by lottery and stone to death
(37:02):
as a person, suggesting that there is some kind of
human urge to simply gang up on a victim and
they in this case. What makes the story so chilling
and so kind of absurd is the victim didn't actually
do something other than being the loser in the lottery.
But what it kind of played out, what continues to
make it fascinating is this dynamic of being part of
(37:25):
a mob united in its victimization of a victim.
Speaker 1 (37:30):
Yeah, so it doesn't only have to do with the violation,
It has to do with the social bonding that results. Okay, great,
what else should everybody know about common knowledge?
Speaker 2 (37:44):
Yes? Well, one of my favorite chapters, the one that
I had one of the most fun writing, was the
one on body language social signals laughing, crying, blushing, staring,
glaring on signals that I think we fall because they
were common knowledge generators. So in case, you know, why
do we blush? The mark twains and men is the
(38:07):
only animal that blushes or needs to and he was
he is right that men are. You know, humanity is
the only animal that plushes. There are other things that
also that make humans unique. We're the only species that
that weeps. We're the only species that laughs. There's a
(38:30):
kind of precursor in chimpanzees in a kind of panting
that a companies play fighting. But you know, it's not
like are exactly the same as our laughter. We are.
Eye contact is really important to humans, and that's probably
why we evolved a white sclera, the whites of our
eyes that other primates don't have. Why we have elongated
(38:51):
eyes so that our position of our eyes can easily
be discerned. So all of these I suggest are effective
because they when you express them, the perceiver knows that
you know that you're expressing them. So in the case
of blushing, you feel the heat of your cheeks from
(39:13):
the inside at the same time that you know that
other people can see them redden from the outside and
they know that you're feeling it. Because what makes blushing
so painful is knowing that other people know that you're blushing,
as when people say you're blushing, which makes people blush
all the more and can even make them blush if
they're not blushing, you know, or or tearing up weeping.
(39:37):
You're seeing the world through the kind of the scrim
of your own tears, and other people can see the
glisten or the trickle of your tears. So these are
cases where I think you're establishing something about your relationship
with the person in a involuntary, unfakable, and undeniable way.
In the case of blushing, it's I know that I've
(39:59):
screwed up by the norms that you hold, and so
even though I've screwed up, better that I know that
I've screwed up than that I just blow off your
norms as if I was some kind of loose cannon
or weirdo or psychopath. In the case of crying, it's
I acknowledge, defeat, surrender, helplessness. I'm not going to fight back.
(40:22):
It's going to be bodily equivalent of raising a white
flag or throwing in the towel in a boxing match. Anyway,
I talk about each one of these displays and why
I think they evolved as a common knowledge generator in
order to ratify a certain kind of social relationship.
Speaker 1 (40:41):
Excellent, Yeah, I love that chapter. Okay, any closing thoughts
about common knowledge?
Speaker 2 (40:47):
Yeah, just is. I think it's a missing piece of
the puzzle of a lot of human life that a
lot of would seem to be arbitrary. Rituals, conventions, hypocrisy
do have a hidden rationale in terms of either generating
or denying common knowledge, including all of the ways in
(41:09):
which we are systematically hypocritical, genteel, polite, dainty. We don't
blurt out things that all of us know privately but
we don't know commonly, and there's a reason for that.
It's necessary to preserve and retain certain social relationships on
which social life depends, and that, as certain comedies point
(41:33):
out where they envision a world in which someone or
everyone is forced to be honest. It quickly becomes a dystopia,
and the characters are glad to go back to a
state in which you don't say everything that you need.
Speaker 1 (41:51):
That was my interview with Stephen Pinker. His new book
is called When Everyone Knows That Everyone Knows, Common Knowledge
and the Mysteries of Money, Power, and Everyday Life. The
book tackles many mysteries of life and psychology centered on
this question of how humans manage to coordinate on scales
(42:11):
that range from two drivers in a game of chicken
to millions of people in a nation. A lot of
the answers lie in this recursive loop of awareness that
we call common knowledge. Pinker shows us in the book
that common knowledge is at least some of the engine
behind laughter, applause, etiquette, trust, diplomacy, and financial markets. And
(42:37):
common knowledge is the difference between a thousand private doubts
and a public turning point in history. Private knowledge lives
in our skulls, but common knowledge spills into the shared
spaces between us, and it's what transforms isolated individuals into
a civilization. In our daily lives, we hardly notice it,
(42:58):
but every time that we have on the correct side
of the road, or laugh at the same moment in
the theater, or rise to our feet in a standing ovation.
We're participating in a recursive dance of shared awareness. The
thing that's so striking is how invisible it generally.
Speaker 2 (43:16):
Is to us.
Speaker 1 (43:18):
But common knowledge is the thread that binds strangers into
this mad, wild, beautiful collective that we call society. Go
to eagleman dot com slash podcast for more information and
find further reading. Join the weekly discussions on my substack
(43:40):
and check out Subscribe to Inner Cosmos on YouTube for
videos of each episode and to leave comments until next time.
I'm David Eagleman, and this is Inner Cosmos.
Why do people speak in innuendo when they're on a date.
Why do dictators try to squelch protests, Why do we
join up with bullies to gang up on an outcast.
Why do humans stand out from the rest of the
animal kingdom by blushing and laughing and crying? And what
(00:25):
does any of this have to do with George Costanza
or when Harry met Sally, or anonymity on social media
or cancel culture, or why we generally don't say everything
we mean. Welcome to Intercosmos with me David Eagleman. I'm
(00:45):
a neuroscientist and author at Stanford and in these episodes
we sail deeply into our three pound universe to understand
why and how our lives looks the way they do.
(01:13):
Today's episode is about a phenomenon known as common knowledge,
which is something that I know and you know, and
we both know that we know it. Now, this could
seem like a very particular sort of thing to pay
attention to, but many psychologists and economists over the past
decades have started to think that a deeper understanding of
(01:35):
common knowledge could explain all kinds of things about human
nature and behavior and societies, and for a very long time.
This has grabbed the attention of my friend and colleague
Stephen Pinker, who just this week has a new book
coming out on common knowledge called When Everyone Knows That
Everyone Knows, And so I called him up to discuss
(01:57):
this topic. I'll take just a moment to frame this
before I begin the interview. At the heart of the
issue is that we are a massively social species. We
form lifelong relationships, and we join clubs, and we're parts
of tribes, and we're citizens of countries. And we're also
a highly intelligent species, and we spend a lot of
(02:18):
our time, usually unconsciously, figuring out who knows what and
what we know in common, and for that matter, thinking
about how we can expand common knowledge with the right signals,
and often how we could hide things from becoming common knowledge.
The key thing to understand for today's conversation is that
(02:39):
common knowledge is not just about a bunch of individuals
each knowing something. It's that each person knows it and
knows that everyone else knows it, and knows that everyone
else knows that they know it, and so on. And
the argument is that it's this ladder of shared awareness
that allows societies to coordinate. Think about something like the
(03:00):
game of chicken, where two drivers speed towards each other.
Each knows the situation, but the critical factor is whether
both drivers know what the other is willing to do,
and whether both know that the other knows. And the
effects of common knowledge stretch from two people all the
way up to countries. For example, history is filled with
(03:22):
moments when private thoughts turned into common knowledge and changed
the world. So, for example, in nineteen eighty nine, East
Germans had long doubted the regime, but it was only
when tens of thousands gathered in the streets when everyone
could see that everyone else had the same doubts. That's
when the Berlin Wall fell. Stock Market bubbles and crashes
(03:45):
run on the same sort of principle. Investors don't care
only about the value of a stock, but about what
everyone else believes everyone else believes about its value. So
this is the type of thing that Pinker's book explores,
all all the ways in which common knowledge permeates everyday life.
(04:06):
Common knowledge, for example, is why etiquette works. You don't
just know the rules, you know that others know them too.
It's why red lights function not because you fear the police,
but because you know that everyone else knows the rule
and is going to stop. It's why children learn to
play Peek a boo, because the delight comes from that
shared loop of I know that, you know that I'm here.
(04:29):
So today we'll explore the phenomenon of common knowledge. Stephen
Pinker is a cognitive scientist and linguist at Harvard and
he's a longtime bestselling author who is famous for illuminating
the hidden structures of human thought and society. His new
book dives into the puzzle of common knowledge, how it arises,
why it matters, and what it reveals about the architecture
(04:52):
of our social minds. Stephen joins me, Now, so, Steve,
we are an intensely social species and there's a lot
that has to happen in order to get us to
coordinate as a result. And this is the thing you've
been thinking about, So tell us how do we coordinate
(05:13):
as a species.
Speaker 2 (05:14):
Well, any two agents who need to coordinate need common knowledge.
The theme of the book, common knowledge, being the state
where I know something, you know it, I know that
you know it, you know that I know it, I
know that you know that I know that you know it,
ad infinitum. Why Because it isn't enough for each party
to know what the other one is going to do,
(05:36):
because the other party guessing what the first one is
going to do may do something complete different. So just
be concrete. If we're going to rendezvous and we don't
generate common knowledge by a conversationalist, and my cell phone
goes dead, so each of us asked to guess where
the other one is going to go. It's not enough
for me to know that you like to go to Starbucks,
because you may know that I like to go to Pete's.
(05:58):
And so if I go to Starbucks, that's where you're
going to go. You might go to pizza because you
think that's where I'm going to go. And well, I
know that, okay, so I'll go to Pietz because Dave
knows that I like to go to pizza. But wait
a sec Dave knows that I know they likes to
go to Starbucks, so he's going to go to Starbucks
after all, and so on. Nothing short of actually blurting
it out in each other's presence will get you on
(06:18):
the same page. Some kind of public perceptible self evidence signal.
That's what is needed for coordination.
Speaker 1 (06:27):
You've, of course spent much of your career studying language,
and so you see language as one way of establishing
that common knowledge give us a sense of that, Yeah,
you know that.
Speaker 2 (06:39):
I'm trying to get you to believe something because you
know that I'm saying something with the intent that you
believe it. That's kind of what language is. So it's
a common knowledge generator when it is something is blurted out.
What got me interested in this whole topic is actually
almost the converse cases in which we try to avoid
(07:00):
common knowledge when we don't say something in so many words,
but we put our meaning between the lines. We count
on our reader to connect the dots. We use euphemism
or innuendo or hinting or beating around the bush or
hilly shallowing, which is a lot of language. That's one
of the reasons it took so long to get computers
to understand language. If you simply parse who did what
(07:22):
to whom based on the subject of the verb and
the object, you're really not going to understand what people
actually meant, such as if you could pass a salt,
that would be awesome. Okay, now think about that. I mean,
that doesn't make it much sense. It would literally be awesome,
And you know, it's not like you're just pondering possible worlds.
That's not the meaning. Everyone knows what the meaning is.
(07:43):
It's give me the salt, and a lot of languages
like that, and linguists have long known it. But the
question is why what do we try to accomplish when
we avoid blurting something what we want out? In so
many words, what I suggest is that the we're avoiding
common knowledge. That is, each one knows what the other
one is doing, but you may not know that the
(08:04):
other one knows that you know that they know, and
that allows you to preserve a certain relationship, relationships being
coordination problems, as we mentioned at the top of the conversation,
a relationship like being friends, being lovers, being a supervisor
in supervisory, being transaction partners. Those are all matters of
common knowledge. We're friends not because we signed a contract,
(08:26):
but because each one knows that the other one knows
that there we're friends, and that can be threatened by
certain things that could become a common knowledge that contradict
the basis of the friendship, like a sexual proposition. So
why do people say things like I want to come
up for Netflix and show, or you want to come
up for coffee when you know, though you know, let's
(08:48):
say it's a man saying it to a woman. You know,
she wasn't born yesterday. She's a grown up, she knows
what it means. But it's still way better than Hey,
you want to come up and have sex, which would
be you know, both parties. You are pretty uncomfortable, even
though would you like to come up for coffee? Doesn't
make them uncomfortable? How come that was the problem that
I took up in a previous book, The Stuff of Thought.
(09:10):
Language is a Window into human nature, which had a
chapter called games People play on language as a window
into social relationships and in trying to figure out why
we don't just blurt out what we mean. Other examples
being say a failed bribe. Let's see you trying to
jump the queue in a restaurant and you slip the
(09:30):
major DA twenty dollars bill and say, I just wondering
if you might have a cancelation, or this is an
important night from you. Is there any way to shorten
my weight? Why don't people just say if I give
you twenty dollars, will you see me? Right? Away or fundraising.
I've seen this a lot at Harvard. I'm sure you've
seen a similar thing where the dean will say to
(09:50):
the rich people in the audience, we're counting on you
to show leadership, to be a friend to the university
instead of the reason we're all here is you're going
to open your checkbook and write, you know, a check
for five million dollars. That's another case where people don't
say what they mean. Why not? And here's the answer
that got me interested in common knowledge. And I've done
(10:13):
studies to back this up that if it's do you
want to come up for coffee? Well, you know, she
knows what he means, and you know obviously he knows
what he means. But does she know that he knows
that she knows? With an innuendo like would you like
to come up for coffee, she could think, well, maybe
he thinks I'm naive, and if I said no, maybe
(10:34):
he thinks, you know, caffeine would keep me up. Even
though she knows that she's turned down a sexual overture,
he knows it as well, but he could not know
why because she knows that he knows. And likewise he
could think, well, you know, maybe she thinks I'm dead,
Maybe she thinks that I think that she's just turned
down coffee. Uh. They can maintain their platonic friendship with
(10:55):
the common knowledge that it's just about companionship. Whereas he
said you want to come up for half sex and
she said no, they can never be platonic friends in
the same way. Again, the intuition is it's out there,
you can't take it back, And I suggest that technically
what's happening is that the blurted out speech generates common knowledge.
(11:18):
Common knowledge is the basis of our relationships. Their coordination, games,
euphemism and innuendo get a message across without generating common knowledge,
and that's why we fall back on it so often.
Speaker 1 (11:30):
Okay, so that's how we sometimes try to mask common knowledge.
Tell us about how common knowledge is useful in society,
society wide, let's say, with public demonstrations and politics and economics.
Speaker 2 (11:44):
Yeah, a lot of our large scale coordination, not just
two friends or Roande going for coffee or agreeing to
be platonic friends, but large scale things like everyone recognizing money,
Like why do I accept a green piece of paper
in exchange for something of value? Well, because I know
that other people will accept it and give me something
(12:07):
of value. Why would they do that, Well, they know
that still other people would accept it. So the value
of currency depends on common knowledge. Everyone knows it's worth something,
and that's what makes it worth something. The fact that
everyone knows that everyone knows it. A lot of power
depends on common knowledge. There are laws, there's courts, there's
a police force, there's a jail. But most of the
(12:28):
time people just follow the law, even though big brothers
watching them twenty four to seven. However, these things can change.
It's not easy to change them when the basis of
power or money is just common knowledge, because everyone has
an interest in keeping up the common assumption. But sometimes
(12:48):
it can unravel. In the case of power, if there
is a public protest, everyone shows up at a public
square at the same time, the same place, everyone sees
everyone else there. Previously, maybe that everyone was resentful of
the system, thought it was inefficient and oppressive. They may
even have suspected that everyone else had the same feeling,
(13:11):
but they didn't know that other people knew that. They
knew they couldn't coordinate by all rising at the same time,
and so the regime could keep them in their place
by preventing common knowledge. And that's why dictators don't allow
freedom of assembly, freedom of the press, freedom of speech,
precisely because they're afraid that people coordinating which they could
(13:34):
only do with common knowledge, could acting together overpower a regime. Likewise,
in the case of going back to money again, if
the value of money depends on common knowledge, then when
the common knowledge is threatened, the value of money can disappear.
And that's what happens when you get hyperinflation, people taking
home their wages in a wheelbarrow because no one will
(13:55):
accept it anymore, or a bank run where people withdraw
their savings, not necessarily because they think that there's anything
wrong with a bank, but as long as there's a
rumor that other people think that there's a problem with
the bank, and they're withdrawing their money out of fear
that still other people will withdraw their money, it suddenly
becomes rational to withdraw your money while the bank still
(14:17):
has money to withdraw. And that can cause a bank
to fail, that can cause the whole economy to fail.
That's what happened in nineteen twenty nine. And so when
Roosevelt said the only thing we have to fear is
fear itself. He was stating a theorem of common knowledge
that was quite literally true, that what people had to
fear was fear itself, and the fear of fear, the
recursive fear, the common knowledge, could actually change the value
(14:41):
of those financial institutions.
Speaker 1 (14:45):
So here's something I wanted to dig in with you
about after reading your book. How do we think about
false common knowledge? By which I mean, let's imagine that
you and I engage in a public protest and we
look around and we see a thousand people around us.
We say, look, everybody clear feels this way, but we're
not aware of that across town there's a larger protest
with ten thousand people in it, and we have the
(15:07):
impression that everyone feels the same way we do about something.
Speaker 2 (15:10):
I mean that technically be common belief rather than common knowledge,
But different pools of people can have different common beliefs,
and there can also be common misconceptions where prior to
the protest, there are cases where people think that everyone
else believes something. In fact, everyone could believe that everyone
else believes someone something and no one actually believes it,
(15:33):
sometimes called a pluralistic ignorance. Or a spiral of silence.
Speaker 1 (15:37):
What's an example of that.
Speaker 2 (15:39):
A classic case study of pluralistic ignorance in social psychology
was when some psychologists interviewed the guys in the fraternity.
They found that every one of them thought that it
was really stupid to drink so much that you pass out,
but everyone thought that all the other frat bros thought
it was cool. No one actually thought it was cool,
(15:59):
but that all the others thought it was cool. And
there are probably a lot of cases like that. I mean,
an extreme case would be The Emperor's New Clothes, where
everyone thought that everyone else thought that who were seeing clothes,
no one actually saw clothes, And it took the little
boy blurting it out generating common knowledge, for the common
(16:19):
misconception to flip into common knowledge. The Emperor's New Clothes
is a story about common knowledge. The boy wasn't telling
anyone anything they didn't already know, but it was changing
the state of their knowledge because now everyone knew that
everyone else knew, and that changed their relationship with the
Emperor from a deference to scorn and ridicule.
Speaker 1 (16:59):
I do worry a little bit, though, about people assuming
politically common knowledge and saying, Hey, if I just make
some innuendo, everyone will understand what I mean by this,
because that often doesn't work, especially now.
Speaker 2 (17:14):
Well, the thing about innuendo is that it has to
be calibrated so that it is recognized by a kind
of willing recipient, but can be denied by an unwilling recipient.
So it has to be calibrated in that zone, and
there can be errors in either direction. Where there's an
(17:35):
episode of Seinfeld where George Costanza is invited up for
coffee and says no because he's got to get to
work early the next morning, and then as he's walking out,
he says, oh, my god, coffee doesn't mean coffee. Coffee
in sex. So there's the Costanza problem that it could
be so subtle that it goes over the head, or
(17:56):
there could be conversely, it's so blatant that the the
unwilling hearer calls you on it again. You know, all
of these things, by the way, are worked out in fiction,
in comedies, comedies of manners, situation comedies. They kind of
allow us to exercise our facility for recursive mentalizing, that is,
(18:19):
getting inside the head of other people, getting inside the
head of other people and so they're often worked out
that so often were drives fictional plots. But the opposite
is when when Harry met Sally, and Harry, you know,
early on, is kind of complimenting Sally and they just
met kind of a little too insistently, and then she
(18:39):
blows the listle. She says, you're coming on to me,
which leads to a wonderful discussion of common knowledge. I mean,
not not in those words where he says, okay, let's
say I was coming on to you. What are we
going to do? I take it back? Okay, I take
it back, and she says, you can't take it back.
He says, what do you mean you can't take it back?
You know, what are we going to do? Call the
(18:59):
cop and she says, it's out there. It's too late,
So it's out there. That is a metaphor for common knowledge.
That is something that's out there, is something that you
see other people see, you see them see it. And
direct speech or even in this case, indirect speech that
was not indirect enough. It kind of exceeded that. The
(19:22):
cutoff is out there, and when it's out there, it
changes the nature of the relationship. They were no longer
just near strangers, platonic friends. He had turned it into
a sexual relationship, which you rebuffed.
Speaker 1 (19:37):
Great, So I want to return for just a second
to literature, which you mentioned fictions, because I made the
argument on this podcast little while ago that I'm not
so worried about AI completely taking the job of writers.
And I listened five different reasons, but one of them
had to do with the fact that we could all
(19:57):
generate totally bespoke literature, just like Kings of Yesteryear would do.
But we lose something there, which is that a big
part of literature is the social glue, the fact that
everyone else has read the same story. I don't want
my Game of Thrones to have a different outcome than
your Game of Thrones. So my question to you is,
what is the reason we desire common knowledge so much?
Speaker 2 (20:20):
I think it's a great example, and people may not
remember that back in the nineties, when the internet first
became a thing, there was the idea that you could
dial in whatever ending to a story you wanted. That
fiction would be, movies would be the same. Everyone could
watch that movie. Maybe let's they didn't take off. And
I think it's the reason that you identified, namely part
(20:43):
of the experience of art is that it's common knowledge.
You know about something at the same time you know
that everyone else knows about it, and that's what gives
you something in common that can reinforce a social relationship.
With friendship, a movie with friends, you talk about it
with friends, and the common experience is one of those
(21:05):
things that kind of go makes friends friends. They go
through things together, they share common interests. The basis, the
common knowledge, that's the tacit basis of friendship is that
we're kind of there's a kind of a mind mild,
even a you know, a body meld, where that we
(21:25):
are in physical proximity, We hug, we shake hands, all
the more intense and romantic relationship.
Speaker 1 (21:31):
Okay, So I want to return and dig in just
a little on this point because I'm fascinated by this
about false common knowledge what I'm calling that or a
misconception about it. So, for example, recently, Charlie Kirk was
assassinated in broad daylight, and if you look on X
and if you look on blue Sky, you find very
(21:53):
different stories about that. And presumably the people who are
tweeting or blue skying are thinking, hey, this is great.
We have shared common knowledge. But you in fact have
two groups of people. I'm exaggerating a little bit the difference,
but you have different groups that have beliefs that they
believe are shared by everybody. Just one second example. This
(22:17):
My grandmother I remember many years ago in Florida said
I can't believe that so and so just one governor,
because I don't know anybody that voted for him. And
it was true, of course she didn't know anybody, but
it doesn't mean that the majority of the state didn't
vote for him.
Speaker 2 (22:33):
Nonetheless, Yeah, I mean common knowledge, or more accurately, in
a lot of these cases, is common belief, That is,
you believe something, you believe that other people believe that
you believe it, and so on. Is relative to a network,
a community which can be disconnected from another network, and
the common knowledge is often generated since none of us
experience everything firsthand. In fact, on for politics, we experience
(22:56):
almost nothing firsthand, and we read about it, we hear
about it. If the sources are disjoint, then the pools
of common knowledge within each of these networks could be disjoined.
And that happens partly from social media, as even feeds
within a platform, but even more so when they're different
platforms like X versus Blue Sky, or in the case
(23:17):
of cable news, do you watch Fox News or do
you watch CNN or do you watch MSNBC. So one
of the users I take up in the book, and
this intersects with my interest in academic freedom and freedom
of speech in another part of my life where I
co founded and I'm the co president of the Council
and Academic Freedom at Harvard. Why is free speech so
(23:40):
important and all the more so in a country? Why
is freedom of speech enshrined in the First Amendment to
the American Constitution, Freedom of the press, freedom of assembly.
So what is it about speech that can be so
threatening to a dictator? You might think, Well, the dictator
would be tend to let people bitch and moan all
(24:01):
they want. He's what with the guns, And as Mao said,
power comes out of the barrel of a gun. So
why should a public protest or a critical editorial be
so threatening to a dictator? Well, the reason is, as
Gandhi said in the eponymous movie, he says to a
(24:26):
British officer in the end, you will leave because there's
simply no way that one hundred thousand Englishmen can control
three hundred and fifteen million Indians if the Indians refuse
to cooperate. So that's just a truth about numbers then,
But it raises the question, how do you get three
hundred and fifteen million people cooperating or in this case coordinating. Well,
some public event demonstration where you're protesting, you can see
(24:52):
everyone else protesting, and everyone can see everyone else. You know,
the time is now a prominent public uh declaration you know,
Jacques or an article. Everyone knows now that it's public
that everyone hates the regime and people can, you know,
either storm the palace or just refuse to work or
(25:15):
to cooperate. And so dictators don't want that to happen.
They want to prevent the generation of common knowledge, which
is why police states control both public assembly and public media.
I give a joke. I recount a joke from the
era of the Soviet Union in which a man is
handing out leaflets in Red Square and of course they're
(25:35):
sure enough the KGB arrested. They take them back to headquarters,
only to discover that these leaflets are blank sheets of paper,
and they think, what is the meaning of this? And
he says, what's there to say, it's so obvious. So
that's a joke about common knowledge. Namely, he was being
subversive because by the very act just handing out leaflets
didn't matter what they said. That now everyone who accepted
(25:58):
the leaflets accepting seeing everyone else except the belief that
they all knew that there was something to protest, and
they didn't have to be told what it was because
they knew privately what it was. The act of communication
was that giving it out in a public square made
the private knowledge common, and that was threatening to the regime,
which is why, in a case of life imitating a joke,
(26:22):
Putin's regime has arrested people for carrying blank science.
Speaker 1 (26:28):
I'm sorry to return to this point, but if you
stood on a street corner and said I'm protesting, and
you handed out blank sheets of paper, the lefties would
think one thing from the blank sheet, and the right's
would think another thing. And so in an ideal sitution,
I mean, we look at the Soviet regime as a failure,
and so we say, okay, it was obvious what he
(26:49):
meant by that. But I'm interested in the fact that
we each have very different internal models. Let's say, with
politics and so the transmission of common knowledge isn't so
easy in a sense.
Speaker 2 (27:03):
Well, yes, I mean it depends on a conspicuous public
signal and in general from a trusted source and who
trusts who can vary between interconnected but disjoint networks of people.
But it's not, you know, it's not the case that
everyone goes that own way. Otherwise we wouldn't have society,
(27:24):
we wouldn't have science, we wouldn't have markets, we wouldn't
have currency.
Speaker 1 (27:28):
But we do have parties. We do have two different
parties that increasingly disagree more and more we do.
Speaker 2 (27:34):
Yes, I mean that, As I said, there can be
the common belief within semi disconnected networks, within each of
which you have common belief, but not necessarily in the
the entire group. The general phenomena are that common knowledge
is generated by public signals that people see when they
(27:58):
know that everyone else sees sees themselves seeing it. And
again that can be relative to pop the population and
the connected network that sees each other seeing something at
the same time.
Speaker 1 (28:12):
So tell us about cancel culture and also why cancel
culture is more possible in a world where people can
hide behind keyboards.
Speaker 2 (28:20):
Yes, I have a chapter in the book called the
Canceling Instinct, and it does touch on my interest in
academic freedom, but the point of the chapter isn't so
much to make the case for academic freedom, though I
do reprise that, but as a psychologist, to ask, why
is there an urge to censor, to cancel, to punish
(28:40):
people for their opinions. Now, of course that's been true
for all of human history, or heretics have been burned
at the stake or crucified. But you think that in
universities of all places, for the arena where we ought
to be, not treat beliefs as sinful. May be mistaken,
(29:01):
maybe illogical, but then you point it out, why do
you try to destroy the person who's ventured that opinion.
That's the phenomenon of cancel culture, and I suggest it's
because a combination of two psychological phenomena. One of them
is that even though the whole basis of science and
(29:23):
scholarship is there is a truth, we have means to
try to approach it. We may be mistaken, but we're
not bad people because we're mistaken. That you believe things
to the extent that there's good evidence for, good arguments
for it, that whole complex of beliefs is kind of
weird in human history. And the more common attitude is
(29:49):
for most people most of the time, is your beliefs
are a reflection of who you are, whether in particular
what tribe you belong to, and whether you're a good person,
who usually means upholding the sacred beliefs of your tribe.
Now that is poison for science and for scholarship and
for academia. But it is the way that people think
(30:11):
that the beliefs I mean putting aside beliefs about here
and now, I mean there are you know, people don't hallucinate.
They know, you know there's food in the fridge. There
isn't food in the fridge. But when it comes to
more bigger questions, where did humans come from? Why is
their disease? Why are their revolutions? Why is their wealth
(30:34):
and inequality? Things that we academics tend to think can
be answered by the methods of science and scholarship. But
most people is what you believe signals what tribe, what
coalition you belong to, And you're bad if you have
the wrong belief So if you have that kind of
(30:54):
built in flaw in human belief, then there can be
norms as to what you believe in what you don't believe.
And norms are matters of common knowledge. They exist because
people believe they exist. They can be threatened if people
flout them and get away with it. So and we
(31:29):
have everyday social norms. You don't go around naked, you
don't make you pass gas in public, you don't tell
ethnic jokes anymore, you don't insult people's appearance to their face.
All these norms are held up just because it isn't done,
and everyone knows that it isn't done. Conversely, if it
is done, the norm can unravel. So people often feel
(31:53):
the need to prop up norms by if noting when
they're flouted in public and then punishing the violator in public.
And the punishment has to be public for it to
prop up the norm, which is why we used to
have public hangings and pillories and stocks and crucifixions. Only
(32:15):
if you have everyone seeing that the person is punished,
could the norm survive well. I think we now have
an equivalent, often an electronic equivalent, in social media, where
if someone does flow a norm, that is, they express
an opinion that goes against what you take to be
the moral convictions of your tribe. People feel the urge
(32:37):
to punish it in public, and that's really easy to
do on social.
Speaker 1 (32:41):
Media and the anonymity of being behind the keyboard. I think,
you know, it's just like the trolley dilemma, where if
you have to push the person with your hands, it's different.
You activate these motional networks and you're less likely to
do that. But if you have to pull the lever
so that only one person gets killed instead of five people,
(33:01):
then most people are perfectly willing to do that at
a distance. And it strikes me it's the same thing
with the anonymity.
Speaker 2 (33:07):
Well, that's right. And it also and this does relate
to another common knowledge phenomenon, that is that our social relationships.
Are we friends? Are we lovers? Are we boss and subordinate?
Are we neighbors, members of a civil society? A lot
(33:28):
of these are reinforced by common knowledge generators. Eye contact, handshakes, laughter, blushing,
eye contact, things that can't be denied. That is, you
look someone in the eye, you're looking at the part
of them that's looking at the part of you that's
looking at the part of them that's looking at the
(33:48):
part of you, ad infinitum. So it's an eye contact
is a common knowledge generator, and the common knowledge that
these signals generate tend to be things like, well, we're
all acting like we're members of a community. So indeed,
when those signals are present because you're face to face,
(34:09):
then that can restore the norms of how you deal
with a person in a peer group, namely, you don't
insult them to your face. Without those common knowledge generators,
such as in the anonymity of a keyboard, then you
can insult people, you can denigrate them, you can try
to destroy the reputations in a way that would be
kind of unthinkable in a face to face situation.
Speaker 1 (34:31):
There's one piece I want to return to about cancel culture,
which is why everybody jumps on the bandwagon. You had
a section in your book about moral condemnation and why
it's better to join the bullies than to take the
risk of being bullied.
Speaker 2 (34:46):
Yeah, yeah, give us a sense exactly. I mean, it's
a kind of a playground dynamic that many of us
remember sometimes with shame, when we may have joined the
bullying mob and out of fear of becoming the kid
that everyone picks on and there is there's an equivalent
in academias. I had to say where I mean, it
(35:07):
has no place because we're all in it together trying
to find the truth. But you get the instant petition
with six hundred signatures, which can usually gin up on
social media. There are enough grad students in the country
that you can get get this is to sign some
condemnatory petition. But I think it is some of the
same dynamic, and there is a dynamics. Sorry to keep
(35:30):
relating things to common knowledge, because it is the theme
of the book, the theme of our conversation, but I
do think that it governs many human interactions. There's a
theory from a former post doc online Peter to Sholey
and his former advisor Rob Kurzband that we know no
one is an island. We really want to be part
of some group, some posse, some band of brothers, because
(35:54):
you know we're sitting ducks. If we're isolated, how do
you know which group to join? You don't want to
be on the losing side. If you can find some
sin that someone has committed and you all jointly recognize
that they are a sinner, they've broken some norm some law,
you gang up on them. That's a and it's common
(36:16):
knowledge as you know that the other people recognize that
same violation. It is a basis for forming a coalition,
and people often will band together and to single out
some victim as and there's something that feels right about
being in that band, and it is the basis that
the coalitions could form and the target suffers their kind
(36:38):
of collateral damage. Probably the episode from fiction that kind
of draws that out of the most is the famous
story by Shirley Jackson called The Lottery, came out in
the late forties, often assigned in high school and debated
ever since, where the town folk of a Bucolic village
every year choose someone by lottery and stone to death
(37:02):
as a person, suggesting that there is some kind of
human urge to simply gang up on a victim and
they in this case. What makes the story so chilling
and so kind of absurd is the victim didn't actually
do something other than being the loser in the lottery.
But what it kind of played out, what continues to
make it fascinating is this dynamic of being part of
(37:25):
a mob united in its victimization of a victim.
Speaker 1 (37:30):
Yeah, so it doesn't only have to do with the violation,
It has to do with the social bonding that results. Okay, great,
what else should everybody know about common knowledge?
Speaker 2 (37:44):
Yes? Well, one of my favorite chapters, the one that
I had one of the most fun writing, was the
one on body language social signals laughing, crying, blushing, staring,
glaring on signals that I think we fall because they
were common knowledge generators. So in case, you know, why
do we blush? The mark twains and men is the
(38:07):
only animal that blushes or needs to and he was
he is right that men are. You know, humanity is
the only animal that plushes. There are other things that
also that make humans unique. We're the only species that
that weeps. We're the only species that laughs. There's a
(38:30):
kind of precursor in chimpanzees in a kind of panting
that a companies play fighting. But you know, it's not
like are exactly the same as our laughter. We are.
Eye contact is really important to humans, and that's probably
why we evolved a white sclera, the whites of our
eyes that other primates don't have. Why we have elongated
(38:51):
eyes so that our position of our eyes can easily
be discerned. So all of these I suggest are effective
because they when you express them, the perceiver knows that
you know that you're expressing them. So in the case
of blushing, you feel the heat of your cheeks from
(39:13):
the inside at the same time that you know that
other people can see them redden from the outside and
they know that you're feeling it. Because what makes blushing
so painful is knowing that other people know that you're blushing,
as when people say you're blushing, which makes people blush
all the more and can even make them blush if
they're not blushing, you know, or or tearing up weeping.
(39:37):
You're seeing the world through the kind of the scrim
of your own tears, and other people can see the
glisten or the trickle of your tears. So these are
cases where I think you're establishing something about your relationship
with the person in a involuntary, unfakable, and undeniable way.
In the case of blushing, it's I know that I've
(39:59):
screwed up by the norms that you hold, and so
even though I've screwed up, better that I know that
I've screwed up than that I just blow off your
norms as if I was some kind of loose cannon
or weirdo or psychopath. In the case of crying, it's
I acknowledge, defeat, surrender, helplessness. I'm not going to fight back.
(40:22):
It's going to be bodily equivalent of raising a white
flag or throwing in the towel in a boxing match. Anyway,
I talk about each one of these displays and why
I think they evolved as a common knowledge generator in
order to ratify a certain kind of social relationship.
Speaker 1 (40:41):
Excellent, Yeah, I love that chapter. Okay, any closing thoughts
about common knowledge?
Speaker 2 (40:47):
Yeah, just is. I think it's a missing piece of
the puzzle of a lot of human life that a
lot of would seem to be arbitrary. Rituals, conventions, hypocrisy
do have a hidden rationale in terms of either generating
or denying common knowledge, including all of the ways in
(41:09):
which we are systematically hypocritical, genteel, polite, dainty. We don't
blurt out things that all of us know privately but
we don't know commonly, and there's a reason for that.
It's necessary to preserve and retain certain social relationships on
which social life depends, and that, as certain comedies point
(41:33):
out where they envision a world in which someone or
everyone is forced to be honest. It quickly becomes a dystopia,
and the characters are glad to go back to a
state in which you don't say everything that you need.
Speaker 1 (41:51):
That was my interview with Stephen Pinker. His new book
is called When Everyone Knows That Everyone Knows, Common Knowledge
and the Mysteries of Money, Power, and Everyday Life. The
book tackles many mysteries of life and psychology centered on
this question of how humans manage to coordinate on scales
(42:11):
that range from two drivers in a game of chicken
to millions of people in a nation. A lot of
the answers lie in this recursive loop of awareness that
we call common knowledge. Pinker shows us in the book
that common knowledge is at least some of the engine
behind laughter, applause, etiquette, trust, diplomacy, and financial markets. And
(42:37):
common knowledge is the difference between a thousand private doubts
and a public turning point in history. Private knowledge lives
in our skulls, but common knowledge spills into the shared
spaces between us, and it's what transforms isolated individuals into
a civilization. In our daily lives, we hardly notice it,
(42:58):
but every time that we have on the correct side
of the road, or laugh at the same moment in
the theater, or rise to our feet in a standing ovation.
We're participating in a recursive dance of shared awareness. The
thing that's so striking is how invisible it generally.
Speaker 2 (43:16):
Is to us.
Speaker 1 (43:18):
But common knowledge is the thread that binds strangers into
this mad, wild, beautiful collective that we call society. Go
to eagleman dot com slash podcast for more information and
find further reading. Join the weekly discussions on my substack
(43:40):
and check out Subscribe to Inner Cosmos on YouTube for
videos of each episode and to leave comments until next time.
I'm David Eagleman, and this is Inner Cosmos.
Host
David Eagleman
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