Ammonius, teacher of Plotinos, thus explained the present problem (the union of soul and body): "The intelligible is of a nature such that it unites with whatever is able to receive it, as intimately as the union of things, that mutually alter each other in uniting, though, at the same time, it remains pure and incorruptible, as do things that merely coexist.[367] Indeed, in the case of bodies, union alters the parts that meet, since they form new bodies; that is how elements change into composite bodies, food into blood, blood into flesh, and other parts of the body. But, as to the intelligible, the union occurs without any alteration; for it is repugnant to the nature of the intelligible to undergo an alteration in its essential nature. It disappears, or it ceases to be, but it is not susceptible of change. Now the intelligible cannot be annihilated; otherwise it would not be immortal; and as the soul is life, if it changed in its union with the body, it would become something different, and would no longer be life. What would the soul afford to the body, if not life? In her union (with the body, therefore), the soul undergoes no alteration. Since it has been demonstrated that, in its essential nature, the intelligible is immutable, the necessary result must be that it does not alter at the same time as the entities to which it is united. The soul, therefore, is united to the body, but she does not form a mixture with it.[368] The sympathy that exists between them shows that they are united; for the entirely animated being is a whole that is sympathetic to itself, and that is consequently really one.[369] What proves that the soul does not form a mixture with the body, is the soul's power to separate from the body during sleep; leaving the body as it were inanimate, with only a breath of life, to keep it from dying entirely; using her own activity only in dreams, to foresee the future, and to live in the intelligible world.