If the necessity of the One is proved by the inward differentiation of what seemed most simple, it is also proved by the integration of what seems most divided. In his next essay, our philosopher wanders off from the investigation of what he has just begun, by abruptly starting the question whether all souls are one.[460] This question is, however, most intimately connected with his main theme. He answers it in the affirmative. Strictly personal as our feelings seem, we are, in reality, one with each other, through our joint participation in the world-soul. Love and sympathy among human beings are solely due to this connexion. Plotinus mentions, as another evidence of its reality, the secret affinities called into play even at a great distance by magical spells—an allusion very characteristic of his age.[461] What prevents us from more fully perceiving the unity of all souls is the separateness of the bodies with which they are associated. Matter is the principle of individuation. But even within the soul there is a division between the rational and the irrational part, concentration being the characteristic of the one and dispersion of the other. The latter is fitted by its divided nature for presiding over the bodily functions of sensation and nutrition; and with the dissolution of the body it returns to the unity of the higher soul. There are two ways in which we can account for this pervading unity. It is either as products or as portions of the universal soul that all particular souls are one. Plotinus combines both explanations. The world-soul first gives birth to an image of itself, and then this is subdivided into as many partial souls as there are bodies requiring animation. On extending our survey still wider, we find that the existence of a thing everywhere depends on its unity.[462] All bodies perish by dissolution, and dissolution means the loss of unity. Health, beauty, and virtue are merely so many different kinds of harmony and unison. Shall we then say that soul, as the great unifying power in Nature, is the One of which we are in search? Not so; for preceding investigations have taught us that soul is only an agent for transmitting ideas received from a higher power; and the psychic faculties themselves are held together by a unifying principle for which we have to account. Neither is the whole sum of existence the One, for its very name implies a plurality of parts. And the claims of the Nous to that distinction have been already disproved. In short, nothing that exists can be the One, for, as we have seen, unity is the cause of existence and must therefore precede it.