Okay. There is a gap. Call this Hume's Gap. I just made that up. [writing on board]
The gap is between the level of confidence
that is justified by reason in my belief that A causes B, and here's the gap, and [writing on board]
my level of confidence that A causes B that I actually have, that's 100 percent.
It seems like such a small thing to quarrel over, and I suppose if we were inclined to
criticize philosophers for straining at gnats we might criticize Hume for this.
But I think Hume has a fairly good response: he says, "Look, I'm just trying to understand
why human minds do what they do. And I can't find the answer in reason.
The only way I find the answer is to say it must be custom or habit that makes up this
missing .001 percent." Let's pause about this.
There's something interesting here, between what reason demands and what human psychology,
meaning what we actually do, does.
And the gap here, (my numbers are arbitrary but there is some non-zero gap, are you guys
with me on this?)
You see the problem here: I treat very very high probabilities as though they were certainties,
and I can't help doing this.
I gave the example last time of me snapping my fingers and putting the lights out.
Constant conjunction, right?
"Past performance is no guarantee of future results." But after a while past performance
is what I'm going with.
Because I have to, I *have* to. My nature compels me to do this.
I think I'm going to take the flip side of this with another example.
It's tough to think now that this is more than 12 years ago: the financial crisis.
Some of you guys probably were in elementary school when this happened.
[Laughter.]
Yeah, '08, yeah. All right, don't, don't, don't tell me, I can only take so much.
The financial crisis was caused in part by reckless trade of derivatives.
Forgive me, if some of you were in the industry I suppose you could you can [correct] me on
this, but my memory is that there were financial products that had been created, bundles of
risky financial products, that are being traded.
And they're products that have a very minuscule chance of failing, but the downside risk when
they fail is enormous.
And of course what happened in '08 was that a whole bunch of them failed at the same time.
That's why it's called a black swan event: something... who would have thought that every
single one of these things would go bad at the same time?
There's a .0001 percent chance that it goes bad, but if it goes bad we lose everything,
the entire company collapses.
But I'd take that deal.
Why, why pass off on a chance of excellent returns on the *remotest* possible chance?
Why? What's happening here?
If a probability can be minimized enough, I will treat it as though it were zero.
That's just a principle of human psychology.
I think this is actually built now into regulation of markets, that we are incapable of reacting
in a practical way to very very minuscule levels of risk.
We can't price it into our behavior.
You would think the market would price it in, the market would say: "Well, these things
that have this 0.001 chance of *destroying* the company that invests in them would trade
at a discount against things that lack that risk, would have maybe a slightly lower return,"
but [shakes head] nope.
Human beings psychologically are incapable of accounting for that small level of risk.
That's the sort of flip side of this: if I can minimize this enough, people will treat
it as non-existent. And I can profit in the transaction.
Does this ring anybody's... ring a bell in anybody's memory?
[unintelligible] Yeah, you know, we're incapable... So we have lines that do this, and so Hume's
answer is that what bridges this gap is habit, custom, human nature, just what we do.
The best way I can think of to put it, and put it not in Hume's terms, is exactly in
terms of the, um... the financial crisis.
A massive... a risk that can be made small enough will be treated as non-existent, even
though it's not non-existent.
I know rationally it's not non-existent, I can't price it into my behavior.
Same thing happens here: causality, constant conjunction, that gets me up to 99 percent...
I'll just run with it like it's a hundred, even though rationally I'm not justified.
Hume says this shows that our beliefs about causal reasoning and our process of induction
are based upon some... rely crucially upon this habit of human minds.
So on page 596, just to go to the text... on 595 he announces the principle is custom or habit.
"Wherever repetition of any particular act or operation produces a propensity to renew
the same act or operation without being compelled by any reasoning or process of the understanding,
we always say that the propensity is the effect of custom." So he's adapting a word from social life.
That was 595 right. 596 left at the very top: "All inferences from experience," I'm sorry, "All inferences
from experience therefore are effects of custom, not of reasoning." Yes it's just a dagger
aimed right at David Hume's [Kant's] heart, okay?
Or David Hume's [Kant's] going to experience it in that way. I'm sorry, Immanuel Kant.
Kant is going to come and say, "No, that's not the case, reasonings from experience are
*not* custom.
There is something rational to them, but I have to reconfigure the entire idea of what
human rationality consists in to make that work."
Just to call your attention to a few passages.
597 left column, middle of the page: "All belief of matter of fact or real existence
is derived merely from some object present to the memory or senses and a customary conjunction
between that and some other object." He calls it farther down that paragraph "as unavoidable
as the feeling of passion of love." Just as we fall in love, we feel things... we rebel
against pain, right? When I feel pain I just pull my hand away: that's instinct.
When I see constant conjunction in my experience, I impute causal power to it.
I say, "Oh the fire has this sort of inner mysterious power...." I haven't perceived anything
in fire that tells me it has the power to cause heat.
All I've perceived is hot fire, repeatedly.
"All these operations are a species of natural instincts which no reasoning or process of
thought and understanding is able either to produce or prevent." It's what we do.
It's what we do. Induction is what we do.
This is going to be a particular case [writes on board] of a phrase that Hume will use in
another context.
He will talk about the human mind spreading itself over objects. Maybe another word
I could use which would be more familiar to us: we are projecting.
We are taking some operation of human psychology, some thing that our minds do, and we are reading
it into nature, we're reading it into the being of things, and saying, "Fire has this
inner power of causing heat." It has no such inner power!
It's just you and your monkey brain, your human minds, which perceive it to be so.
Over and over again, this will be Hume's diagnosis of metaphysics, of theories of the self: it's
all the human mind misperceiving its own properties and projecting them out into the world and
acting as though they actually are properties of beings other than human beings, outside of itself.
So the sort of philosophical illusion of metaphysics is based upon this idea, this habit of human
psychology, of reading itself and its properties into nature and then speaking
about those properties as though they were real stable realities in nature.
We realize, come David Hume, that neither empirically nor analytically can we justify such beliefs.
It's really been about us all along.
That's what it is, it's what it has always been, always will be.
Now there's self-knowledge for you!
You wanted self-knowledge, as a philosopher? I've given you self-knowledge.
But the world looks different from the way you thought it was.
Now you need to be more disciplined in your use of language.
Or I think that maybe you need to be a Pyrrhonian like David Hume: "Okay, too bad for reason.
It was a nice run, but it was... it didn't work, it doesn't work, it doesn't do what
the ambition for it was." Again, this is very characteristic of modern
and even contemporary approaches to the classical tradition: it's based upon an error about
human minds and human reasoning and human psychology.