10.8 — Descartes to Hume: The Modern Break

Something changes in the seventeenth century, and the change is about where authority comes from.

Before: you establish a claim by showing it follows from an authoritative text or an accepted system.

After: you establish it by starting from something you can be certain of yourself, and building.

And the person who makes the break most explicitly is a French soldier sitting alone in a heated room in Germany in 1619.

Descartes

His problem: he noticed that a great many things he had been taught were false, and that he had no way of telling which.

His method: doubt everything that can possibly be doubted, and see what survives.

And he is systematic about it.

The senses deceive — sticks look bent in water, distant towers look round. So sensory evidence goes.

Dreams are convincing while you are in them (9.8 runs the same argument). So the whole external world might be a dream, and it goes.

And then the strongest version: suppose there is a powerful deceiver whose whole purpose is to mislead me. Then even mathematics might be a trick — perhaps I am made to go wrong every time I add.

What survives that?

One thing. If I am being deceived, I exist to be deceived.

Cogito, ergo sum. I think, therefore I am.

What the cogito actually establishes

Less than people think, and Descartes knew it.

It establishes that something is thinking, right now. It does not establish that there is a persistent self, that there is a body, that there is a world, or that any of your memories are real.

And Descartes spends the rest of the Meditations trying to get from that one point back to the world — via an argument for God's existence and then the claim that a perfect God would not deceive him. Almost nobody thinks that part works, and it is generally agreed that he never got out of the room.

Which leaves the modern problem: a certain starting point and no reliable route from it to anything else.

The dualism

And his other legacy, which caused more trouble than the doubt.

Two kinds of substance. Mind, which thinks and has no extension in space. Body, which is extended in space and does not think.

And the immediate objection, put to him at the time by Princess Elisabeth of Bohemia in a correspondence worth knowing about: how does an unextended thinking thing move an extended one? If mind has no location and no physical properties, what does it push?

Descartes suggested the pineal gland as the meeting point, which is not an answer.

And he never answered Elisabeth's objection. It is the same interaction problem Samkhya has (9.4), and it is the reason mind-body dualism is a minority position now — not because anybody proved it false, but because nobody could say how it works.

The rationalists and the empiricists

And the eighteenth century divides into two camps over one question: where does knowledge come from?

Rationalists — Descartes, Spinoza, Leibniz — say reason. Some knowledge is available prior to experience, and mathematics is the model.

Empiricists — Locke, Berkeley, Hume — say experience. The mind starts empty and everything is written on it by the senses.

Spinoza

Worth a paragraph because he is the most rigorous and the most personally admirable.

Excommunicated from the Amsterdam Jewish community at twenty-three, in the harshest terms on record, for his views. He ground lenses for a living, refused a professorship to keep his independence, and died at forty-four.

His system: there is only one substance, and you can call it God or Nature. Everything that exists is a mode of it. Mind and body are not two substances but the same thing under two descriptions — which dissolves Descartes' problem rather than solving it.

And his ethics: freedom is not doing what you want; it is understanding why you want it. A person driven by passions they do not understand is not free. Understanding the causes of your own emotions changes them — which is a claim modern therapy makes and which is close to 9.4's discrimination.

Locke

The mind at birth is a blank sheet. All ideas come from sensation or from reflection on the operations of the mind.

And his political work matters more than his epistemology. Government exists by the consent of the governed, to protect life, liberty and property, and a government that violates that may be replaced. The American Declaration of Independence is Locke, nearly verbatim, and Volume VIII covers what followed.

Berkeley

Takes empiricism to its conclusion and gets a strange result.

If all we ever have is perceptions, what grounds the claim that there is matter behind them? Nothing. So there is no matter — to be is to be perceived.

Things continue to exist when unobserved because God perceives them.

Almost nobody accepts this and nobody can refute it cleanly. Samuel Johnson's famous response was to kick a stone and say "I refute it thus," which is not an argument and which everybody remembers.

Hume

And the empiricist who followed the logic all the way and produced results that alarmed everybody, including himself.

Causation

His most famous argument.

You see one billiard ball strike another and the second move. What do you actually observe?

One event, then another event, in that order, repeatedly.

You do not observe a necessary connection. There is no perception of "causing." You observe conjunction and you supply the necessity.

And where does the supplying come from? Habit. You have seen it many times and you expect it, and that expectation is a fact about your mind rather than about the world.

This is Charvaka's problem of induction (9.10), arrived at independently, and it has never been solved. Every scientific law rests on the assumption that the future will resemble the past, and there is no non-circular argument for that assumption — any argument for it will itself use induction.

The self

And the other one, which is more startling.

Look for the self. What do you find?

"When I enter most intimately into what I call myself, I always stumble on some particular perception or other — of heat or cold, light or shade, love or hatred, pain or pleasure. I never can catch myself at any time without a perception, and never can observe anything but the perception."

Therefore there is no self, only a bundle of perceptions in constant flux.

That is 6.7, in Edinburgh, in 1739. The Buddha's argument, reached independently, from the same procedure — look for it, report that the search fails.

And Hume was not satisfied with it. In an appendix he admits he cannot make his account of personal identity work and does not know how to fix it, which is an unusual thing for a philosopher to publish.

Is and ought

And the observation that changed ethics.

He notices that writers on morality proceed for a while with ordinary claims about what is the case, and then suddenly all the sentences are about what ought to be — and the transition is never explained.

You cannot derive an ought from an is. No collection of facts about the world entails a value, without a value premise smuggled in somewhere.

This is the is-ought problem and Part 13 has to deal with it.

What the period established

Three things.

That you can start from your own experience and reason rather than from authority. This is the move, and everything modern rests on it.

That the mind-body relationship is a genuine problem, and 15.2 says it still is.

And that empiricism, followed honestly, undermines a great deal that everybody assumed — causation, the self, and the derivation of values. Hume did not intend to be destructive; he followed the argument.

Kant said Hume woke him from his dogmatic slumber, and 10.9 is the response.

What to carry from this page

Doubt everything you can and see what survives. You will get less than you hoped, and the exercise is worth doing once.

You do not observe causation. You observe conjunction and supply the rest. Which is worth remembering every time you are certain that one thing produced another.

Look for the self and you find perceptions. Two traditions, two millennia apart, same procedure, same result.

And no set of facts entails a value on its own. Every argument that jumps from "this is how things are" to "therefore you should" has a hidden premise, and finding it is the most useful analytical habit in this Part.

Next: 10.9 — the man who tried to put it all back together, and the moral rule you can state in one sentence.