Marsilio Ficino’s Platonic Theology, Volume II

2That the soul is a substance is also evident from this: through it a living creature receives a definite and substantial nature, together with the name of its species and genus. Through this soul one creature is a dog, through that soul another is a horse, and through a different soul another is a man. An accidental quality comes to its subject after the subject is already complete in its species. The soul, however, fashions its own body for itself, preserves it once made, restores it when it fails, and binds the conflicting elements into one. When the soul departs, the body collapses, and neither its former constitution nor its species is retained. The nutritive soul, then, must necessarily be a substance of this kind. Nor should we say that the soul which is solely nutritive constructs the body and that afterward, when the body is already complete, a sensitive soul comes to it as a kind of accident. For a body suited to a sensitive soul must possess instruments for sensing and for moving from place to place. The nutritive soul, insofar as it is nutritive, would make only the instruments of nourishment; another soul would make other instruments for the sake of those powers whose use they are to serve. Yet there are not two souls in the same body, one of which fashions instruments for the other. The soul that nourishes is the same soul that senses. Indeed, disturbances of the senses hinder the work of nourishment or increase it: sorrow in the imagination weakens that work, while joy strengthens it, as though there were one soul in man to which both offices belong. The soul is therefore a substance, because it is the craftsman of the body, not its handmaid. It is therefore not a constitution.