300. Intellectual Knowledge. -- Scholasticism is peripatetic in its theories on the nature of the intellectual act and on its essential difference from sensation: whilst the sense knows only the particular and the contingent, the intellect reaches realities, whether substantial or accidental, by divesting them of the individualizing features with which the things of sense are affected (abstraction). The object of the concept, because abstract, admits of generalization, i.e., of being referred to an indefinite multitude of individuals. The intellect can know all Being, owing to this process of abstraction. But its strictly proper and natural object is the quiddity or essence of sensible things; it is only by analogical and negative concepts that we grasp the nature of the soul and of supra-sensible beings in general. The existence of the Ego alone is an intuitive datum, implied in all conscious activity: according to the expression of St. Augustine, "ipsa (anima) est memoria sui".

But if the human understanding perceives in things universal realities only, must we refuse it all direct knowledge of the individual? So St. Thomas thinks, and his conclusion is logical. To meet the difficulties which at once spontaneously arise, he admits that the intellect has a certain knowledge of singular beings in virtue of some sort of a "refiexio" on the sense data, or an "applicatio" the nature of which is one of the obscure points of Thomism. Other scholastics take the course of admitting in the intellect, in addition to abstract knowledge, an intuitive knowledge, about which we shall hear more later.

Abstraction was and is the keystone of scholastic ideology. It also offers a definite solution of the criteriological problem and of the question of the Universals. The metaphysical aspect of the question and the "three states of the essence" have been already referred to. This latter formula, so often explained by St. Thomas, bears more directly on the psychology of the problem: the essence of a thing can be the object of a threefold subjective consideration, secundum esse in natura, secundum se, secundum esse in intellectu. "Secundum esse in natura," it is singular (287); "secundum se," it is the simple quiddity of the thing, abstracting from the mental or extramental existence of the latter; "secundum esse in intellectu," it is universalized, conceived in relation to an indefinite multitude of beings in which it can be found. The process of universalization as such is subjective; it is superadded to a previous process of abstractive segregation, which apprehended the objective being or essence.

The genesis of concepts was another favourite subject of research during the thirteenth century. The formula "nihil est in intellectu quod prius non fuerit in sensu," enunciated the sense-origin of ideas and the dependence of even the highest operations of our soul upon the organism. The determining influence of the intelligible object on the passive faculty of the understanding and the causal intervention of the sense image (phantasma) and of a special abstractive force or faculty (intellectus agens) to produce this determination, are regarded as indispensable for the generation of thought. The theory of St. Augustine, who did not acknowledge this causal intervention, is abandoned.^{1} St. Thomas criticizes Plato's ideogeny and declares the function which the latter assigns to the object to be insufficient ("excitant animam intellectivam ad intelligendum").^{2} His criticism tells with equal force against the explanation of the Augustinians. The scholastics are furthermore unanimous in maintaining, against the Arabian philosophers, that the principles of thought are internal to the soul: they reject the separate existence of the intellectus agens and the intellectus possibilis. But the question of the respective functions of the two intellects and of the phantasm remained open to free discussion.

According to St. Thomas Aquinas and Duns Scotus, it is the sense-reality that acts on the understanding through the intermediate agency of the phantasm, but this latter exercises only an instrumental causality, conjoined with, and subordinate to, the efficiency of an immaterial faculty, the "intellectus agens". By virtue of this concurrence of a higher force, the sense-image -- and in ultimate analysis the external object -- call forth the exercise of the passive understanding ("species intelligibilis impressa"), an exercise of immanent activity in which the cognitive representation properly socalled is achieved and completed ("species intelligibilis expressa").^{3} It is noteworthy that from the beginning of the thirteenth century the false theory of the "spiritualized phantasm" gained credit with a large number of scholastics (244). It implies an erroneous notion of the "species intelligibilis," arising from the incorrect conception of the "species sensibilis" referred to above. This latter solution of the ideological problem, leading as it does to the overthrow of scholastic spiritualism, has given rise to interminable misunderstandings (see below).

{1} Matthew of Aquasparta is one of the few scholastics who adopt the Augustinian ideology pure and simple (258).

{2} S. Theolog., i., 84, 6.

{3} This terminology is common among the contemporaries of St. Thomas. St. Thomas himself usually means by species the species impressa; the species expressa he prefers to call the verbum (mentale).