Aristotle’s Theory of Motion

Aristotle defines motion as such: ‘The fulfillment of what exists potentially, in so far as it exist potentially, is motion.’ (Phy., Γ, 1, 201a10-11) He defines it again in the same chapter: ‘It is the fulfillment of what is potential when it is already fully real and operates not as itself but as movable, that is motion. What I mean by ‘as’ is this: Bronze is potentially a statue. But it is not the fulfillment of bronze as bronze which is motion.’ (Phy., Γ, 1) 2) Motion: not a real thing Aristotle believes that ‘there is no such thing as motion over and above the things’ that is supposed to mean that motion cannot be something else than his categories: ‘It is always with respect to substance or to quality or to quantity or to place that what changes changes. But it is impossible to find anything common to these which is neither ‘this’ not quantum nor quale nor any of the other predicates. Hence neither will motion and change have reference to something over and above the things mentioned, for there is nothing over and above them.’ (Phy., Γ, 1, 200b32-201a3) In fact, it is what is moved that is a reality for Aristotle and not the motion itself: ‘Motion is known because of that which is moved, locomotion because of that which is carried. What is carried is a real thing, the movement is not.’ (Phy., Δ, 11) 3) Three items in each motion Aristotle distinguishes three items in each motion (Phy., E, 4): a) ‘That which’ moves; (Note: It is this item that makes a motion a unitary motion. (Phy., Δ, 11)) e.g. a man or gold b) ‘That in which’ the movement occurs; e.g. a place or an affection c) ‘That during which’ the movement takes place; e.g. time Based on the second item, Aristotle distinguishes three kinds of motion: quantitative, qualitative and local which are in respect of the three categories of quantity, quality and place. (Phy., E, 1) However, Aristotle speaks of four things in respect of which change takes place adding substance to the three mentioned categories. (Phy., Γ, 1, 200b32-35) It seems it is based on the differentiation of that in which motion takes place in these four types that Aristotle distinguishes four kinds of motion. (Phy., Γ, 1, 201a11-15): a) Alteration: the motion of what is alterable qua alterable b) Increase and decrease: the motion of what can be increased and what can be decreased c) Coming to be and passing away: the motion of what come to be and pass away d) Locomotion: the motion of what can be carried away Alteration happens in qualities, increase and decrease in quantities, coming to be and passing away in substances and locomotion in place. 4) Problem of motion as an element Discussing why Pythagoreans put motion in their column of indefinites, Aristotle somehow hints to the problem of understanding motion due to its non-elemental character: ‘The reason why they put motion into these genera is that it is thought to be something indefinite and the principles in the second column are indefinite because they are privative: none of them is either ‘this’ or ‘such’ or comes under any of the other modes of predication. The reason in turn why motion is thought to be indefinite is that it cannot be classed simply as a potentiality or as an actuality- a thing that is merely capable of having a certain size is not undergoing change, nor yet a thing that is actually of a certain size, and motion is thought to be a sort of actuality, but incomplete. The reason for this view being that the potential whose actuality it is is incomplete. This is why it is hard to grasp what motion is. It is necessary to class it with privation or with potentiality or with sheer actuality, yet none of these seems possible. There remains then the suggested mode of definition, namely that it is a sort of actuality, or actuality of the kind described, hard to grasp, but not