History of Western Philosophy - Bertrand Russell [320]
regretfully. There has been, in quite recent times, an attempt to escape from this subjectivism by the philosophy known as instrumentalism, but of this I will not speak at present. With this exception, modern philosophy has very largely accepted the formulation of its problems from Descartes, while not accepting his solutions.
The reader will remember that St Augustine advanced an argument closely similar to the cogito. He did not, however, give prominence to it, and the problem which it is intended to solve occupied only a small part of his thoughts. Descartes's originality, therefore, should be admitted, though it consists less in inventing the argument than in perceiving its importance.
Having now secured a firm foundation, Descartes sets to work to rebuild the edifice of knowledge. The I that has been proved to exist 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 judgment, 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 outside things. (The word 'idea' includes sense-perceptions, as used by Descartes.) Ideas seem to be of three sorts: (1) those that are innate, (2) those that are foreign and come from without, (3) those that are invented by me. The second kind of ideas, we naturally suppose, are like outside objects. We suppose this, partly because nature teaches us to think so, partly because such