has been inferred from the fact that I think, therefore I exist while I think, and only then. If I
ceased to think, there would be no evidence of my existence. I am a thing that thinks, a substance
of which the whole nature or essence consists in thinking, and which needs no place or material
thing for its existence. The soul, therefore, is wholly distinct from the body and easier to know
than the body; it would be what it is even if there were no body.
Descartes next asks himself: why is the cogito so evident? He concludes that it is only because it
is clear and distinct. He therefore adopts as a general rule the principle: All things that we
conceive very clearly and very distinctly are true. He admits, however, that there is sometimes
difficulty in knowing which these things are.
"Thinking" is used by Descartes in a very wide sense. A thing that thinks, he says, is one that
doubts, understands, conceives, affirms, denies, wills, imagines, and feels--for feeling, as it occurs
in dreams, is a form of thinking. Since thought is the essence of mind, the mind must always
think, even during deep sleep.
Descartes now resumes the question of our knowledge of bodies. He takes as an example a piece
of wax from the honeycomb. Certain things are apparent to the senses: it tastes of honey, it smells
of flowers, it has a certain sensible colour, size and shape, it is hard and cold, and if struck it emits
a sound. But if you put it near the fire, these qualities change, although the wax persists; therefore
what appeared to the senses was not the wax itself. The wax itself is constituted by extension,
flexibility, and motion, which are understood by the mind, not by the imagination. The thing that
is the wax cannot itself be sensible, since it is equally involved in all the appearances of the wax
to the various senses. The perception of the wax "is not a vision or touch or imagination, but an
inspection of the mind." I do not see the wax, any more than I see men in the street when I see hats
and coats. "I understand by the sole power of judgement, which resides in my mind, what I
thought I saw with my eyes." Knowledge by the senses is confused, and shared with animals; but
now I have stripped the wax of its clothes, and mentally perceive it naked. From my sensibly
seeing the wax, my own existence follows with certainty, but not that of the wax. Knowledge of
external things must be by the mind, not by the senses.
This leads to a consideration of different kinds of ideas. The commonest of errors, Descartes says,
is to think that my ideas are like out-