PHYSICS with other examples of kinesis: the gradual heating of a body, the carving of a statue, the healing of a patient, the building of a house (3 201a10–15) Motion, he says, is a notion diYcult to grasp, and this is because it is as it were halfway between straight potentiality and straight actuality He sums up his account in a slogan, saying that motion is an incomplete or imperfect actuality of an imperfect potentiality (3 201b31) Being at B would be the perfect actuality; moving to B is the imperfect actuality The potentiality for being at B is the perfect potentiality; the potentiality for moving to B is the imperfect potentiality Motion is a continuum: a mere series of positions between A and B is not a motion from A to B If X is to move from A to B, it has to pass through any intermediate point between A and B; but passing through a point is not the same as being located at that point Aristotle argues that whatever is moving already has been moving If X, travelling from A to B, passes through the mid-point K, it must already have passed through an earlier point J halfway between A and K However short the distance between A and J, that too is divisible, and so on ad inWnitum At any point at which X is moving, there will be an earlier point at which it was already moving (cf Ph 236b33–5) It follows that there is no such thing as a Wrst instant of motion Aristotle’s account of motion is embedded within a careful analysis of the semantic properties of Greek verbs English, unlike Greek, has a special continuous form of each tense The diVerence between ‘He runs’ and ‘He is running’ is clear enough in English So too is the diVerence between ‘Whatever moves has moved before’ (which is doubtful) and ‘Whatever is moving has been moving before’ (which is true) In Greek Aristotle has to go to some pains to make clear that he is talking not about whatever moves, but whatever is moving He does, however, maintain not just that whatever is moving has been moving before, but that whatever is moving has moved before (Ph 237b5) For Aristotle, there are some verbs that signify kineseis (motions) and some that signify energeiai (actualities) (Metaph h 1048b18–36) Kinesis, as has been said, includes not only motion but many diVerent kinds of change and production: Aristotle gives as examples learning something, building a particular house, walking to a particular place As examples of energeiai he gives seeing, knowing, and being happy He distinguishes between his two classes of verbs by means of subtle linguistic points 185