92. When Kant observes that the subject in which the thought inheres is only indicated in a transcendental way, without its properties being discovered, and that, therefore, we do not know the simplicity of the subject itself, he declares a fact which is in some sense admissible, but he deduces from it a false consequence. It is true that we only know the substance of the soul by the presence of the internal sense, and by its relation to its acts; and consequently that the soul in itself abstracted from all the phenomena which we experience, is not given in immediate intuitions, and that when we arrive at this point we are reduced to the idea of a simple being, but this indeterminateness, and vagueness, in the knowledge of the substance of the soul, does not prevent our knowing its simplicity, if this simplicity is revealed by the internal sense, and also by the nature of the phenomena by which we know the thinking subject. 93. Some persons may believe that the indeterminateness of the knowledge of the substance of the soul is a fact recently discovered by the German philosopher; but it is easy to show that it had been observed long before, and is laid down in a very special and interesting manner in the writings of St. Thomas. This eminent metaphysician proposes the question whether the intellectual soul knows itself by its essence, _utrum anima intellectiva seipsam cognoscat per suam essentiam_, and after the various remarks on intelligence, and the intelligibility of objects, he solves it in these remarkable words: "Our understanding does not know itself by its essence, but by its act; and this in two ways: in one way, in particular; inasmuch as Sortes or Plato perceives that he has an intellectual soul, because he perceives that he understands: in the second way, in general; inasmuch as we consider the nature of the human mind in the act of the understanding. But it is true that we derive the judgment and efficacy of the knowledge by which we know the nature of the soul, by the light of the divine truth of which our intellect participates, and in which are contained the reasons of all things, as was said above. Hence, Augustine says, in the ninth book on the Trinity: We have intuition of the inviolable truth by which we perfectly determine, as far as possible, not what the mind of each man is, but what it should be according to the eternal reasons. But there is a difference between these two cognitions, for, to have the first, we only need the presence of the mind, which is the principle of the act by which the mind perceives itself, and, therefore, we say that it knows itself by its presence; but for the second, the presence of the mind is not sufficient, but a careful and subtile investigation is necessary. Hence many are ignorant of the nature of the soul, and many also have erred on the nature of the soul; wherefore in the tenth book on the Trinity, Augustine, speaking of this investigation, says: The soul should not