KNOWLEDGE view of the Matterhorn, or a taste of a vintage port are all, in his terminology, thoughts Thinking, for Descartes, includes not only intellectual meditation, but also volition, emotion, pain, pleasure, mental images, and sensations The feature which all such elements have in common, which makes them thoughts, is the fact that they are items of consciousness ‘I use this term to include everything that is within us in such a way that we are immediately conscious of it Thus, all the operations of the will, the intellect, the imagination and the senses are thoughts’ (AT VII 160; CSMK II 113) ‘Even if the external objects of sense and imagination are non-existent, yet the modes of thought that I call sensations and images, in so far as they are merely modes of thought, do, I am certain, exist in me’ (AT VII 35; CSMK II 34) These thoughts, then, are the basic data of Descartes’ epistemology One passage brings out very strikingly how the word ‘thought’ for Descartes applies to conscious experience of any kind: It is I who have sensations, or who perceive corporeal objects as it were by the senses Thus, I am now seeing light, hearing a noise, feeling heat These objects are unreal, for I am asleep; but at least I seem to see, to hear, to be warmed This cannot be unreal, and this is what is properly called my sensation; further sensation, precisely so regarded, is nothing but an act of thought (AT VII.29; CSMK II 19) These apparent sensations, possible in the absence of a body, are what later philosophers were to call ‘sense-data’ The viability of the Cartesian system depends on whether a coherent signiWcation can be given to such a notion.2 In the third Meditation Descartes singles out an important class of thoughts, and gives them the name ‘ideas’: ‘Some of my thoughts are as it were pictures of objects, and these alone are properly called ‘‘ideas’’—for instance, when I think of a man, or a chimera, or the sky, or an angel, or God’ (AT VII.37) The word ‘idea’ is now at home in ordinary language, but it was a new departure to use it systematically, as Descartes did, for the contents of a human mind: hitherto philosophers had commonly used it to refer to Plato’s Forms, or to archetypes in the Mind of God Crudely, we can say that, for Descartes, ideas are the mental counterpart of words ‘I cannot express anything in words, provided that I understand what I say, without its thereby being certain that there is within me the idea of what is signiWed by the words in question’ (AT VII.160) See Ch below 122