Whether a sensitive soul can be produced through the power of the semen.
Next one inquires whether a sensitive soul can be produced through the power of the semen.
1. And it seems not. Every form that is perfect and not composite is produced per se without generation, because generation pertains to composites. But the sensitive soul is perfect; otherwise, it would not move the body. And it is not a composite because it is a form of the body. Therefore, it is produced per se without matter.
2. In addition, nothing acts beyond its species. But the generative power [ potentia], which lies within the sensitive soul, is numbered among the powers of the vegetative soul. Therefore, the generative power does not go outside its species, and therefore, does not extend to the sensitive soul.
3. In addition, each thing is generated from one like itself. If, then, the sensitive soul is produced from the semen, then the sensitive soul or a part of it will be in the semen. But the conclusion is false because neither the sensitive soul nor a part of it exists without a part of the body, and semen is not a part of the body.
4. In addition, if the sensitive soul were produced by the power of the semen, then the complete sensitive soul or that power would either remain, or not. If it remains, then either it is the same as the sensitive soul, or different. If the same, then the same thing is both generating and generated. If different, then it is useless. If it does not remain, then it has worked for its own corruption, as was said above.
To the contrary. Just as a form that is produced from the elements of the world is related to the power that is in them, so too the form of a perfect animal is related to the power that is in the semen, as the Philosopher implies at the end of this eighteenth chapter of this book. But those that are generated from the elements of the world, like those begotten from putrefaction, proceed from a power that is in the elements themselves. Therefore, even the forms of perfect animals proceed from a power which is in the semen, but this form is the sensitive soul. And so it is correct to argue in this way: Just as the power in the elements of the world relate to imperfect animals, so does the power in the semen relate to perfect animals. But the power in the elements of the world produces a form of the imperfect animals. Therefore, the power which is in the semen produces a form of the perfect animals.
To this, one must reply that the sensitive soul is produced from a power that is in the semen. For if the sensitive soul were a form existing per se and having an operation per se, it would come to be per se because a thing relates to being and operation in the same way that it does to becoming. But this is not the case, because it neither exists nor operates without the body, since it is destroyed when the body is destroyed, and this is why it is necessary that the sensitive soul come to be by means of other corporeal forms which do not come to be per se but only per accidens in the fashioning of bodies. Thus in the seventh book of his Metaphysics the Philosopher says that forms neither exist nor not-exist without generation and corruption. This is why it is necessary that the sensitive soul is produced in being through a certain nature and a power that is in the body and in the semen.
But one must understand that the more perfect a form is, the more it extends itself to many things, just as the hotter something is, the more it can heat other things from a distance. Thus some things are generated from themselves and without a medium, and some are generated through a medium and without a medium. The first are the elements and those near to them, as fire only generates fire by means of contact and so without a medium. But living things can generate both through a medium or without one. They act without a medium as when the flesh takes part in nourishment, seeing that flesh generates flesh and bone generates bone. And they act with a medium, as in the case of generation in the proper sense of the word, because in generation they generate through the medium of semen, in which the power of the one generating exists. Nor is it important whether the one generated is said to come into being from the one generating or from the semen, just as it is not important to say that something comes to be from a principal agent or from an instrument, because an instrument acts only by the power of the principal agent.
1. On to the arguments. To the first, one must reply that a sensitive soul is perfect, but it does not subsist per se, and this is why it does not come into being per se.
2. To the second argument one must reply that one acting on its own power does not go beyond its species, but one acting on another's power can go beyond its own species, but it does not act by that one's power. Thus although the generative power is numbered among the powers of the vegetative soul, if, however, the seed in which the power of the soul exists comes forth from a plant, this power acts by the power of the entire plant, and if it proceeds from an animal, then it acts by the power of the entire animal. And this is why, because it acts by the power of the whole and not by its own power, it can produce not only the vegetative but also the sensitive soul.
3. To the third argument one must reply that neither the soul nor a part of the soul is in the semen, as was said, but rather all that is in the semen is merely a certain power capable of producing a soul, and this is why it is not necessary that some part of the body be in the semen, since this power is in the semen or the spirit, which is frothy body. And this power is not only the power of the soul itself, but is also a power of a superior agent, like the sun. Thus power is in the semen in two ways: as a power of both a universal and a particular agent, and this is why the Philosopher says that "a human generates a human, and the sun does as well."
4. To the fourth argument one must respond that the active power is in the semen of the father and the matter for the fetus is provided by the female. Moreover, the vegetative soul is in this material immediately as first act, but not as the second act, just as the sensitive soul exists in one who is sleeping, and by means of the power that is in the sperm this material is digested and completed and formed until the introduction of the sensitive soul. But when the sensitive soul is introduced, certain principal parts are already being formed, like the heart and the liver, in which there is the power for disposing and preparing the material for the reception of the forms of the other members. Thus, once the sensitive soul has been introduced, the power that is in the sperm is not needed any longer, because then the embryo can sufficiently develop itself through its own nutritive and augmentative action.