The discussion of these difficulties, however, is a task appropriate to a different investigation: let us return to the elements of which bodies are composed. The theories that there is something common to all the elements, and that they are reciprocally transformed, are so related that those who accept either are bound to accept the other as well. Those, on the other hand, who do not make their coming-to-be reciprocal-who refuse to suppose that any one of the elements comes-to-be out of any other taken singly, except in the sense in which bricks come-to-be out of a wall-are faced with a paradox. How, on their theory, are flesh and bones or any of the other compounds to result from the elements taken together?
Indeed, the point we have raised constitutes a problem even for those who generate the elements out of one another. In what manner does anything other than, and beside, the elements come-to-be out of them? Let me illustrate my meaning. Water can come-to-be out of Fire and Fire out of Water; for their substratum is something common to them both. But flesh too, presumably, and marrow come-to-be out of them. How, then, do such things come to-be? For (a) how is the manner of their coming-to-be to be conceived by those who maintain a theory like that of Empedocles? They must conceive it as composition-just as a wall comes-to-be out of bricks and stones: and the Mixture, of which they speak, will be composed of the elements, these being preserved in it unaltered but with their small particles juxtaposed each to each. That will be the manner, presumably, in which flesh and every other compound results from the elements. Consequently, it follows that Fire and Water do not come-to-be out of any and every part of flesh. For instance, although a sphere might come-to-be out of this part of a lump of wax and a pyramid out of some other part, it was nevertheless possible for either figure to have come-to-be out of either part indifferently: that is the manner of coming-to-be when both Fire and Water come-to-be out of any and every part of flesh. Those, however, who maintain the theory in question, are not at liberty to conceive that both come-to-be out of flesh in that manner, but only as a stone and a brick both come-to-be out of a wall-viz. each out of a different place or part. Similarly (b) even for those who postulate a single matter of their elements there is a certain difficulty in explaining how anything is to result from two of them taken together-e.g. from cold and hot, or from Fire and Earth. For if flesh consists of both and is neither of them, nor again is a composition of them in which they are preserved unaltered, what alternative is left except to identify the resultant of the two elements with their matter? For the passing-away of either element produces either the other or the matter.
Perhaps we may suggest the following solution. (i) There are differences of degree in hot and cold. Although, therefore, when either is fully real without qualification, the other will exist potentially; yet, when neither exists in the full completeness of its being, but both by combining destroy one anothers excesses so that there exist instead a hot which (for a hot) is cold and a cold which (for a cold) is hot; then what results from these two contraries will be neither their matter, nor either of them existing in its full reality without qualification. There will result instead an intermediate: and this intermediate, according as it is potentially more hot than cold or vice versa, will possess a power-of-heating that is double or triple its power-of-cooling, or otherwise related thereto in some similar ratio. Thus all the other bodies will result from the contraries, or rather from the elements, in so far as these have been combined: while the elements will result from the contraries, in so far as these exist potentially in a special sense-not as matter exists potentially, but in the sense explained above. And when a thing comes-to-be in this manner, the process is combination; whereas what comes-to-be in the other manner is matter. Moreover (ii) contraries also suffer action, in accordance with the disjunctively-articulated definition established in the early part of this work. For the actually-hot is potentially-cold and the actually cold potentially-hot; so that hot and cold, unless they are equally balanced, are transformed into one another (and all the other contraries behave in a similar way). It is thus, then, that in the first place the elements are transformed; and that (in the second place) out of the elements there come-to-be flesh and bones and the like-the hot becoming cold and the cold becoming hot when they have been brought to the mean. For at the mean is neither hot nor cold. The mean, however, is of considerable extent and not indivisible. Similarly, it is qua reduced to a mean condition that the dry and the moist, as well as the contraries we have used as examples, produce flesh and bone and the remaining compounds.