On Generation and corruption   

must also investigate 'contact'. For action and passion (in the proper

sense of the terms) can only occur between things which are such as to

touch one another; nor can things enter into combination at all unless

they have come into a certain kind of contact. Hence we must give a

definite account of these three things- of 'contact', 'combination',

and 'acting'.

Let us start as follows. All things which admit of 'combination'

must be capable of reciprocal contact: and the same is true of any two

things, of which one 'acts' and the other 'suffers action' in the

proper sense of the terms. For this reason we must treat of

'contact' first. every term which possesses a variety of meaning

includes those various meanings either owing to a mere coincidence

of language, or owing to a real order of derivation in the different

things to which it is applied: but, though this may be taken to hold

of 'contact' as of all such terms, it is nevertheless true that

contact' in the proper sense applies only to things which have

'position'. And 'position' belongs only to those things which also

have a Place': for in so far as we attribute 'contact' to the

mathematical things, we must also attribute 'place' to them, whether

they exist in separation or in some other fashion. Assuming,

therefore, that 'to touch' is-as we have defined it in a previous

work'-'to have the extremes together', only those things will touch

one another which, being separate magnitudes and possessing

position, have their extremes 'together'. And since position belongs

only to those things which also have a 'place', while the primary

differentiation of 'place' is the above' and 'the below' (and the

similar pairs of opposites), all things which touch one another will

have 'weight' or 'lightness' either both these qualities or one or the

other of them. But bodies which are heavy or light are such as to

'act' and 'suffer action'. Hence it is clear that those things are

by nature such as to touch one another, which (being separate

magnitudes) have their extremes 'together' and are able to move, and