Such is the doctrine of St. Thomas. Cardinal Cajetan, one of the most penetrating and subtile minds that ever existed, has a commentary on this passage, worthy of the text. These are his words: "Two things expressly follow, from what is said in the text. The first is, that our intellect has of itself the faculty of understanding. The second is, that our intellect has not of itself the faculty of being understood. Hence the order of intellect is below the order of intelligible beings. For if the perfection, which our intellect has of itself, is sufficient to understand, but not to be understood, it necessarily follows that greater perfection is required in a thing to be understood than to understand. And because St. Thomas saw this consequence, which at first sight does not seem true, and might even be objected to him, he excludes this apprehension, by showing that this must be admitted to be true not only by the Peripatetics, from whose doctrine it results, but also by the Platonists." But afterwards, in answer to an objection brought by Scotus, called the Subtle Doctor, he adds: "But because in order to understand an intellect and an intelligible object are required, and the relation of the intellect to the intelligible, is the relation of the perfectible to its perfection, since the intellect in act consists in its being itself the intelligible thing, as is evident from what has been said above; it follows that immaterial beings are divided into two orders, intellects, and things intelligible. And as the intelligible consists in perfective immateriality, it follows that any thing is intelligible inasmuch as it is immaterially perfective. That intelligibility requires immateriality is shown by this, that no material thing is intelligible, unless, inasmuch as it is abstracted from matter.... It has already been shown that any thing is intelligible by this, that not only itself, but others, also, are in the intelligible order, either in act or in potentiality; it is thus nothing more than to be perfected or perfectible by the intelligible." 123. This theory may be more or less solid, but it is in either case something more than ingenious; it raises a new problem in philosophy of the highest importance: to assign the conditions of intelligibility. It has moreover the advantage of being in accordance with a fact attested by experience; this fact is the difficulty experienced by the mind in knowing itself. If it is immediately intelligible, why does it not know itself? What condition is wanting? Its intimate presence? It has not only presence but identity. Perhaps the effort to know itself? But the greater part of philosophy has no other end than this knowledge. By denying immediate intelligibility to the soul, we can explain why so great a difficulty is involved in ideological and psychological investigations, by showing the reason of the obscurity experienced in passing from direct to reflex acts.