Now, how can this be done? I have told you: it is because man is not a simple being. Fix this truth firmly. Man is triple; and it is according as his volitive unity operates in one or the other of his modifications that he is led on to see, in such or such a way. Plato has said it, following Pythagoras, and I say it to you not only following Pythagoras and Plato, but following all the sages and all the theosophists of the world. Plato places in the superior and spiritual modification, composed of the _same_, that is to say of the indivisible substance of the universe, the _hegemonicon_,[526] or the intellectual assent; in the inferior and material modification, composed of the _other_ or the _diverse_, that is to say, of the divisible substance, the _physicon_,[527] or the physical sense perception; in the median modification or the soul, properly speaking, composed of essence, that is to say, of the most subtle parts of matter elaborated by the spirit, the _logicon_,[528] or the moral, logical, or reasonable sentiment. One finds in Plutarch the _résumé_ of the doctrine of a philosopher named Sylla, who, admitting, as did Plato, that man is composed of spirit, soul, and body, said that the body drew its origin from the earth, the soul from the moon, and the spirit from the sun.[529] But without disturbing ourselves for the present, with the origin of these three parts, since assuredly the earth, the moon, and the sun, which this philosopher has assigned them for principles, are things very difficult to understand in themselves, let us be content with knowing, as I have already said, that these three great modifications which form the human Quaternary manifest themselves by sensation, sentiment, and assent, and develop the principal faculties of the instinct, the understanding, and the intelligence. The instinct is the seat of common sense; the understanding is that of reason; and the intelligence, that of sagacity or wisdom. Men can never acquire any science, any real knowledge, if the assent is not determined by favour of the intelligence which elects the principle and places it with sagacity; for one can really know or understand only that to which the intelligence has given consent. All the results that the understanding, deprived of intelligence, can procure by means of reason are only opinions, those of these results which are rigorously demonstrated in the manner of the geometricians are identities; common sense transported even into the understanding can give only notions, the certainty of which, however founded it may be upon experience, can never surpass that of physical sensation, whose transient and limited authority is of no weight in the assent of intelligible truths.