On Generation and corruption   

body's place-whence it clearly follows that to every body there will

correspond a void of equal cubic capacity.

As a general criticism we must urge that to postulate pores is

superfluous. For if the agent produces no effect by touching the

patient, neither will it produce any by passing through its pores.

On the other hand, if it acts by contact, then-even without pores-some

things will 'suffer action' and others will 'act', provided they are

by nature adapted for reciprocal action and passion. Our arguments

have shown that it is either false or futile to advocate pores in

the sense in which some thinkers conceive them. But since bodies are

divisible through and through, the postulate of pores is ridiculous:

for, qua divisible, a body can fall into separate parts.



9



Let explain the way in which things in fact possess the power of

generating, and of acting and suffering action: and let us start

from the principle we have often enunciated. For, assuming the

distinction between (a) that which is potentially and (b) that which

is actually such-and-such, it is the nature of the first, precisely in

so far as it is what it is, to suffer action through and through,

not merely to be susceptible in some parts while insusceptible in

others. But its susceptibility varies in degree, according as it is

more or less; such-and such, and one would be more justified in

speaking of 'pores' in this connexion: for instance, in the metals

there are veins of 'the susceptible' stretching continuously through

the substance.

So long, indeed, as any body is naturally coherent and one, it is

insusceptible. So, too, bodies are insusceptible so long as they are

not in contact either with one another or with other bodies which

are by nature such as to act and suffer action. (To illustrate my

meaning: Fire heats not only when in contact, but also from a