The sensory/intellectual continuum

Two philosophical traditions – the rationalist and the empiricist – came together in Kant's philosophy, not in an inconsistent jumble but in a coherent synthesis of truths drawn from each. Underlying this positive achievement is a crucial negative one, namely Kant's avoiding of a certain error which was common to the empiricists and the rationalists. I shall chart this error in the present section and the next, and Kant's correction of it in §§6–8. Topics related to this will occupy the rest of the chapter.

The error is that of assimilating the sensory to the intellectual aspects of the human condition. No one would fail to distinguish seeing a man from thinking about men, hearing a whistle from understanding a lecture about whistles, feeling running water from drawing a conclusion; but the philosophers I am concerned with put all these matters on a continuum, representing as a difference of degree what is really one of kind.

A common vehicle for this mistake is the word ‘idea’. Some philosophers have said that ‘ideas’ are what one has or is confronted with in ordinary sense-experience, in hallucinations, in some kinds of imagining and so on, and that they are also involved in thinking and understanding – so that having a meaning for a word is associating it with an ‘idea’, and thinking through a problem is mentally manipulating ‘ideas’. Descartes clearly commits himself to using ‘idea’ as widely as that. He takes the term ‘idea’ to stand for ‘whatever the mind directly perceives’, and he says explicitly that ‘perception’ covers ‘sense-perception, imagining, and even conceiving things that are purely intelligible’. Descartes’ detailed procedures also show him allowing ‘idea’ to sprawl across the whole realm of the mental. On the sensory side, for example, he says: ‘If I now hear some sound, if I see the sun, or feel heat,…I can perhaps persuade myself that these ideas are adventitious’, where ‘these ideas’ are clearly items of sensory intake that occur in hearing, seeing etc. But there is nothing sensory about Descartes’ ‘idea’ of God, when he asks what there is ‘in that idea’, and bases his answer on the fact that ‘By the name God I mean a substance that is infinite, eternal, immutable, independent, omniscient, omnipotent…’.