Whether homogenous [consimiles] parts are generated immediately from the elements.

We have already stated above that the members," etc. In his twelfth book the Philosopher establishes the composition of parts. Therefore, with respect to this, the twelfth book, we first inquire whether similar parts are immediately generated from the elements.

1. And it seems they are. This is because generation is analogous to decomposition [ resolutio], although they differ either according to their causes or their ends, since that "which is first in generation is last in decomposition" and contrariwise. But homogenous parts can be immediately decomposed into elements; therefore, they can also be immediately generated from them.

2. Besides, just as official parts come from homogenous ones, so too do homogenous ones come from the elements. But official parts are generated immediately from the homogenous ones. Therefore, homogenous ones are immediately generated from the elements.

On the contrary: One and the same thing is both the principle of nutrition and of generation, because "we exist from and are nourished by the same things."3 But homogenous parts do not take their nourishment immediately from the elements; therefore, neither are they generated from them.

To this, one must respond that homogenous parts are not generated immediately from the elements, for although prime matter is in potency to every form, it nevertheless cannot receive every form immediately. Thus the Philosopher says in the eighth book of the Metaphysics that wine does not come from vinegar immediately nor does a living being come from a corpse immediately, because wine is generated on a vine. Thus in order for wine to come from vinegar, it would first be necessary that the vinegar be changed into a nutriment for the vine. And, in the same manner, nature proceeds through several intermediaries when producing an animal, since the semen comes from a superfluity of nourishment, the blood from the semen, and the embryo from the blood. Thus, in order for the homogenous parts to come from the elements, it is first necessary that a mixture suitable to nutrition come forth from the elements, and then that mixture is converted into food, and then into chyle (that is, into a humor) and then it can nourish.

1. On to the arguments. To the first argument one should respond that generation and corruption occur differently. For generation has being as its goal, and corruption has non-being, and this is why nature proceeds in an ordered way when generating, but proceeds as if in a disordered way in corruption.

Or one can state it in another way, namely, that when corrupting something, nature uses all the things acquired through generation as if for a single end, and that is why the elements come forth immediately from the homogenous parts, but not contrariwise.

2. To the second argument one should respond that it is not the same for the official parts in respect to the homogenous ones or for the homogenous parts in respect to the elements. For official and homogenous parts are produced from one nature and are informed by one common form, and so too that does not come from the homogenous parts and the elements, and this is why, etc.

Whether the elements exist in act in homogenous parts.

Further one inquires whether the elements may exist in act in homogenous parts.

1. And it seems that they may. For alteration is a change in quality, with the subject remaining the same. But "mixture is a union of altered mixables [miscibilium alteratorum] Therefore, the mixables remain in substance, changed only in quality.

2. In addition, according to the Philosopher in On Generation [and Corruption], a mixture differs from generation and corruption. But if the elements were entirely corrupted in the homogenous parts, then a mixture would not differ from generation and corruption, because there would be a corruption of the mixable and a generation of the mixed.

3. In addition, power does not exist without substance, according to On Heaven and Earth. But in the mixed "the power of the mixables is preserved." Therefore, so too is their substance.

On the contrary. One thing does not really come from several things in act. Therefore, if the elements remained in act, the mixed would not really be one thing.

To this, one must respond that the elements do not remain in act either in homogenous parts or in any mixed things. The reason for this is that contrary forms cannot at one and the same time perfect the same matter, nor, according to the Philosopher in On Generation and Corruption, is any part of the mixed itself mixed. If, then, the elements were present in act in the mixed, they would be present in act in some part of the mixed. But the forms of the elements are contraries, and, as a result, contraries will exist at the same time in the same part, which is false, and therefore, etc.

Moreover, the heat of fire is one thing, against or beyond which the form of fire is not preserved, and the heat of air is something else, beyond which the form of the air does not extend. If, then, the elements exist in act in a mixed thing, there would be two heats of different degrees in the same part. But this contradicts what the Philosopher says in the third book of the Physics. For he says there that the same thing cannot be changed simultaneously by two whitening agents.

Furthermore, if the elements were present in a mixed thing in act, then either some part of one will exist at the same time as, or right next to, another part of the other. If it is at the same time, since an element has its own dimensions, then two dimensions and, as a result, two bodies would exist at the same time, which is false. If it is next to it, then the mixture will only be a juxtaposition. But this is false, since, according to Avicenna, true mixture does exist when the very least part of one touches the very least part of the other.

Nevertheless, the Commentator proposes that elemental forms exist in act in a mixed thing under a certain refraction, remission, and tempering, because their qualities are pushed back from a state of excess. But in order to sustain this view he proposes many false ones, namely, that the elemental forms strive forward and are then pushed back. For he himself proposes that the elements are midway between substances and accidents, which is impossible, because then there would be a mean between contradictories, namely, between being in a subject and non-being in a subject.

1. On to the arguments. To the first, one should respond that for a mixture, it is necessary that there first be an alteration in the mixables, to the extent that the forms of the mixables are expelled and the form of the mixed is introduced. Thus, as long as the mixables are present during the process of alteration, they remain, but once the form of the mixed has been introduced, the alteration ceases, and it is unnecessary for the mixables to remain. Thus a mixture is "a union of previously altered mixables." And if you were to say that only those things that are present in act can be united, and that a mixture is a union, and that they therefore are present in act, one must reply that if you understand by "mixture" a total transformation that occurs beforehand and is accompanied by a boundary, then, with the transformation going on beforehand, the mixables themselves approximate one another, and this is their union. But if we were to understand by "mixture" the final transformation, then that union ought not be referred to the mixables but to their powers.

2. To the second argument one should respond that alteration is a kind of generation. And likewise mixture is a kind of generation. Nevertheless, mixture is to be distinguished from generation properly speaking, because in the proper sense of generation the form of the one overcoming, corrupting, or generating is introduced. But this is not the case in a mixture, and if the four elements, equally disposed to be active or passive, come together for a mixture, then they act or are acted upon, one to the other, so that in the end all will be absent at the same time and one form having the power of all will then be introduced into their materials.

And in this respect there is another difference between a mixture and generation, because the power of the one corrupted is not found throughout the one generated, as the power of water is not present in fire, if fire should come from water. But in a mixture the power of the mixables is preserved throughout, and this is why a mixture differs from generation.

3. To the third argument one should respond that every power reveals its own substance. Thus, if the power of the mixables is in the mixture, this power is not the ultimate, as it is in a mix-able per se. Thus this power of a mixed thing is the power of a subject, but that of a mixable is like that of an efficient cause. Thus the power of a mixable is in the mixture just as the power of the white is in the red and the power of water placed in wine, etc.

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