Descartes’ method of systematic doubt

Diana asked:

Descartes gives a list of things he had previously believed. What are these?

Answer by Craig Skinner

Short answer: his method entails his suspending belief about absolutely everything except one thing, namely,

* because he is doubting, he is thinking, and therefore must exist (‘I think therefore I am’, or, in Latin, ‘cogito ergo sum’).

He hopes to argue his way back to most of his former beliefs by sound reasoning from this single, clear and distinct, indubitable belief, thereby establishing a ‘firm and permanent structure in the sciences’.

Although he makes mention of his method of doubt in Rules for the Direction of the Mind and in Discourse on Method, the definitive account is in his Meditations, specifically Meditation 1 subtitled ‘Of the things which may be brought within the sphere of the doubtful’.

First, he says he must doubt everything learned through the senses (all empirical or a posteriori knowledge as we would say). For the senses can deceive, and also, at any given moment, he can’t be certain he is not dreaming, or that his mind is nor controlled by an ‘evil genius’ which deceives him about everything.

Secondly, he must doubt all truths of reason (rational or a priori knowledge). He feels that, even if dreaming, he knows that 2+3 = 5, but he considers that an evil genius could deceive him about mathematical truths, interfering in his thought every time he adds 2 and 3 so that he is sure (wrongly) that the sum is 5.

The nearest he gets to a list is towards the end of this Meditation, when he says:

‘I shall consider that the heavens, the earth, colours, figures, sound, and all other external things are nought but… illusions and dreams… I shall consider myself as having no hands, no eyes, no flesh, no blood, nor any senses, yet falsely believing myself to possess all these things.’

Having done all this doubting, the only certainty remaining, the Archimedean fixed point as he calls it, was ‘I think therefore I am’ (this exact wording is actually given in his Discourse on Method, but formulations in Meditations are equivalent)

Of course, he didn’t really doubt that there is a world out there, or that he had a body. His scepticism was a ploy (methodological scepticism) to try to put his views on a rational footing. However his arguments back from the cogito to belief in the physical world of concrete things, other people and his own body (with God as the bridge, so to speak), are widely considered unsound or invalid. So the upshot is that one of his main legacies is scepticism rather than its resolution, and strong philosophical scepticism (about matter, the external world, causation and selves) later emerges, for example in the views of Berkeley and Hume.

Craig Skinner at PhiloSophos.com