try to see itself as something absent, but endeavor to distinguish itself as something present; that is, to know its difference from other things, which is to know its quiddity and nature."[49] [49] Non ergo per essentiam suam, sed per actum suum se cognoscit intellectus noster, et hoc dupliciter. Uno quidem modo particulariter, secundum quod Sortes, vel Plato percipit se habere animam intellectivam ex hoc, quod percipit se intelligere. Alio modo in universali, secundum quod naturam mentis humanæ ex actu intellectus consideramus. Sed verum est quod judicium, et efficacia hujus cognitionis per quam naturam animæ cognoscimus, competit nobis secundum derivationem luminis intellectus nostri a veritate divina, in qua rationes omnium rerum continentur, sicut supra dictum est. Unde August. dicit in 9 de Trin. Intuemur inviolabilem veritatem, ex qua perfecte quantum possumus, deffinimus, non qualis sit uniuscujusque hominis mens, sed qualis esse sempiternis rationibus debeat. Est autem differentia inter has duas cognitiones; nam ad primam cognitionem de mente habendam sufficit ipsa mentis præsentia, quæ est principium actus, ex quo meus percipit seipsam: et ideo dicitur se cognoscere per suam præsentiam. Sed ad secundam cognitionem de mente habendam, non sufficit ejus præsentia: sed requiritur diligens, et subtilis inquisitio. Unde et multi naturam animæ ignorant, et multi etiam circa naturam animæ erraverunt. Propter quod August. dicit 10 de Trin. de tali inquisitione mentis, Non velut absentem se quærat mens cernere; sed præsentem quærat discernere; id est cognoscere differentiam suam ab aliis rebus, quod est cognoscere quidditatem, et naturam suam. S. Thom. _Sum. Theol._ P. I. Q., LXXXVII., A. 1. 94. It is to be observed that St. Thomas admits two cognitions of the soul by itself;--that of its presence, as we perceive it in perceiving our thought, _percipit se habere animam intellectivam ex hoc quod percipit se intelligere_; and another which we deduce from the analysis of the intellectual act reasoning from general considerations, and reflecting on the light which the eternal reasons shed upon this fact of experience. This is how St. Thomas explains the knowledge of presence or consciousness contained in the proposition, _I think_; and the general knowledge which we deduce from the same intellectual act in its relations to the unity of the subject exercising it. That this last contains something abstract and indeterminate no one denies; and when Kant calls attention to it, he tells us nothing which the holy Doctor had not already told us when he expressly affirmed that the soul knows itself not in its essence, but in its acts. These few laconic words express all the truth which is contained in Kant's diffuse explanation of the limitation of our cognition to the acts of consciousness, and the absence of the intuitive knowledge of the substance of the soul, the transcendental subject of the thought. CHAPTER XIII.