On Generation and corruption   

be moved by, one another.

The manner in which the 'mover' moves the moved' not always the

same: on the contrary, whereas one kind of 'mover' can only impart

motion by being itself moved, another kind can do so though

remaining itself unmoved. Clearly therefore we must recognize a

corresponding variety in speaking of the 'acting' thing too: for the

'mover' is said to 'act' (in a sense) and the 'acting' thing to

'impart motion'. Nevertheless there is a difference and we must draw a

distinction. For not every 'mover' can 'act', if (a) the term

'agent' is to be used in contrast to 'patient' and (b) 'patient' is to

be applied only to those things whose motion is a 'qualitative

affection'-i.e. a quality, like white' or 'hot', in respect to which

they are moved' only in the sense that they are 'altered': on the

contrary, to 'impart motion' is a wider term than to 'act'. Still,

so much, at any rate, is clear: the things which are 'such as to

impart motion', if that description be interpreted in one sense,

will touch the things which are 'such as to be moved by them'-while

they will not touch them, if the description be interpreted in a

different sense. But the disjunctive definition of 'touching' must

include and distinguish (a) 'contact in general' as the relation

between two things which, having position, are such that one is able

to impart motion and the other to be moved, and (b) 'reciprocal

contact' as the relation between two things, one able to impart motion

and the other able to be moved in such a way that 'action and passion'

are predicable of them.

As a rule, no doubt, if A touches B, B touches A. For indeed

practically all the 'movers' within our ordinary experience impart

motion by being moved: in their case, what touches inevitably must,

and also evidently does, touch something which reciprocally touches

it. Yet, if A moves B, it is possible-as we sometimes express it-for A

'merely to touch' B, and that which touches need not touch a something

which touches it. Nevertheless it is commonly supposed that 'touching'