d. Fourth Conclusion

27. A fourth conclusion, about the distinction of flesh as to species and flesh as to matter, is plain from the third conclusion, because each part of flesh has a certain period of time within the whole, and it has a greater period the purer it is, and a lesser one the more impure it is. For flesh can keep its being in the whole as long as it is able, through its qualities, to resist what corrupts it. Now this period is greater in a part generated first than in one generated later, and each same part is more efficacious in acting in the prior part of a period than in the later part. And this difference must be understood to hold when other things are equal, that is: if a part of flesh was generated from the sort of food that was of a nature to be converted into flesh as equally pure as that from which the flesh was generated, then, provided a proportionate alteration of food is posited, purer flesh is of a nature to be generated from one food than from another.

28. From these points to the fourth conclusion: form bestows being and acting; therefore, a part according to form (a form-part) can be so spoken of as long as it has being according to form, or as long as it has acting according to form. And the second of these implies the first, and not conversely; for a thing more quickly loses action because of imperfection than being. In both respects, whether in this way or that, a form-part is not only a part of form, but includes matter as well as form.

29. Now in the first way [sc. as to being] any part, while it remains in the whole, is said to be a form-part, namely from the beginning to the end of its period, because, that is, it has being for that length of time.

30. In the second way [sc. as to action] it is not said to be a form-part for every part of the period, but for that part of the period for which it has power effective enough that action according to form can belong to it. I do not mean ‘belong to it’ only as it concurs with the action of the whole, nor as it is simply separate from the whole; but I mean that there is present to it in the whole a virtue for the action proper to it, which action it would be able to have as existent in the whole even though it not be considered precisely as it concurs with the action of the whole. And the efficacy of a virtue for action requires a determinate intensive and extensive virtue. For some slight part of virtue could not have its proper action in the whole in this way, but could only concur with the action of the whole, as Aristotle says [On Sense 6.445b31-6a1] about the action on the senses of a hundred thousandth part of a grain of millet.

31. Some determinate extensive quantity of virtue, therefore, is required for this efficacy of action in the whole.

32. Some intensive quantity of virtue is also required because, as was said [n.30], after active virtues decline to such an extent that they yield rather to their contraries than conquer them, the virtue cannot act with its proper action; therefore, in this second way, a species-part is of so much natural quantity and of so much active virtue that its proper action can belong to it, not indeed as it is a supposit outside the whole, but proper to it in such a way that it does merely concur with the action of the whole.

33. In the first way [as to extensive quantity, n.31], a part according to matter is not opposed to a species-part, save as a dead man is opposed to a living man; and thus is the same part said to be a species-part while it remains in the whole and a part according to matter when it is in flux, just as the same man is first said to be a living man and afterwards a dead man.

34. In the second way [as to intensive quantity, n.32], one part among the parts that remain in the whole is a species-part and another part is a part according to matter, because some slight part, to which no action can belong, even if it is at the beginning of its period, is a part according to matter; but a part of quantity sufficient for acting is a species-part - and that if it have virtue efficacious for an acting that requires a quantity of virtue. And contrariwise, a part according to matter is what does not have such efficacy of virtue, however much extensive quantity it may have.