Cartesianism

The claim

I am thinking, therefore I am. Thought is one kind of substance and extension another, and everything physical — including animal bodies — is mechanism.

What it held

Descartes' method is to withhold assent from anything that could conceivably be false, including the evidence of the senses and mathematics, and to see what survives. What survives is that the doubting is happening, and that something is doing it.

From that he rebuilds: a proof of God, then a guarantee that clear and distinct ideas are reliable, then the external world. The circularity of that sequence was pointed out immediately by Arnauld and has been argued about ever since.

The consequence that mattered most was not the cogito but the dualism. If mind is thinking substance and body extended substance, they have no property in common, and how they interact becomes unanswerable. Descartes suggested the pineal gland; Princess Elisabeth of Bohemia wrote to ask how something unextended could move something extended, and his replies to her are visibly worse than the rest of his work.

His followers went in directions he had not intended. Malebranche concluded that only God causes anything. Geulincx proposed two synchronised clocks. And the wholly mechanical physical world he described is the one modern science inherited.

How it argued

Systematic doubt, then deduction from indubitable premises, presented as a first-person narrative of discovery rather than as a treatise.

What it was arguing against

Scholastic Aristotelianism entire — substantial forms, final causes, and the authority of the schools.

Where it disagreed with itself

The Cartesian circle. Mind-body interaction, which the school never solved and which produced occasionalism and pre-established harmony as attempted answers.

Common misconceptions

That the cogito is an inference with a suppressed premise. Descartes says explicitly it is grasped in a single intuition rather than deduced. And the animal-machine doctrine is often overstated: he denied animals language and reason, not sensation, though his followers went further.

How it began

A soldier's winter quarters in 1619, three dreams, and a decision to rebuild knowledge on foundations he had laid himself.

What became of it

Banned at Utrecht and by the Sorbonne, placed on the Index, and dominant anyway for a century before empiricism and Newton displaced it.

Lasting influence

The whole subsequent shape of the mind-body problem is his. Analytic geometry is his. And the modern habit of beginning philosophy from the first-person point of view starts here.

Why it still matters

The hard problem of consciousness is the dualism problem in modern dress, and no consensus solution has arrived in four centuries.

Put another way

A house demolished to the foundations by someone who intends to live in it again.

Where to start

The Meditations with the Objections and Replies. Reading it without them makes it look far less argued than it is.

The surprising bit

Princess Elisabeth's objection — that an unextended thing cannot move an extended one — has never been satisfactorily answered, and Descartes' correspondence with her is where he is most visibly stuck.

In their own words

Connections

Opposed by

Early Scholasticism, British Empiricism

Influenced

Spinozism, French Materialism

The verdict

A method that succeeded and a metaphysics that failed, and the failure has been more productive than most successes.

Sources

• Stanford Encyclopedia of Philosophy