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(Latin intelligereinter and legere — to choose between, to discern; Greek nous; German Vernunft, Verstand; French intellect; Italian intelletto).

The faculty of thought. As understood in Catholic philosophical literature it signifies the higher, spiritual, cognitive power of the soul. It is in this view awakened to action by sense, but transcends the latter in range. Amongst its functions are attention, conception, judgment, reasoning, reflection, and self-consciousness. All these modes of activity exhibit a distinctly suprasensuous element, and reveal a cognitive faculty of a higher order than is required for mere sense-cognitions. In harmony, therefore, with Catholic usage, we reserve the terms intellect, intelligence, and intellectual to this higher power and its operations, although many modern psychologists are wont, with much resulting confusion, to extend the application of these terms so as to include sensuous forms of the cognitive process. By thus restricting the use of these terms, the inaccuracy of such phrases as "animal intelligence" is avoided. Before such language may be legitimately employed, it should be shown that the lower animals are endowed with genuinely rational faculties, fundamentally one in kind with those of man. Catholic philosophers, however they differ on minor points, as a general body have held that intellect is a spiritual faculty depending extrinsically, but not intrinsically, on the bodily organism. The importance of a right theory of intellect is twofold: on account of its bearing on epistemology, or the doctrine of knowledge; and because of its connexion with the question of the spirituality of the soul.


The view that the cognitive powers of the mind, or faculties of knowledge, are of a double order — the one lower, grosser, more intimately depending on bodily organs, the other higher and of a more refined and spiritual nature — appeared very early, though at first confusedly, in Greek thought. It was in connexion with cosmological, rather than psychological, theories that the difference between sensuous and rational knowledge was first emphasized. On the one hand there seems to be constant change, and, on the other hand, permanence in the world that is revealed to us. The question: How is the apparent conflict to be reconciled? or, Which is the true representation? forced itself on the speculative mind. Heraclitus insists on the reality of the changeable. All things are in a perpetual flux. Parmenides, Zeno, and the Eleatics argued that only the unchangeable being truly is. Aisthesis, "sense", is the faculty by which changing phenomena are apprehended; nous, "thought", "reason", "intellect", presents to us permanent, abiding being. The Sophists, with a skill unsurpassed by modern Agnosticism, urged the sceptical consequences of the apparent contradiction between the one and the many, the permanent and the changing, and emphasized the part contributed by the mind in knowledge. For Protagoras, "Man is the measure of all things", whilst with Gorgias the conclusion is: "Nothing is; nothing can be known; nothing can be expressed in speech". Socrates held that truth was innate in the mind antecedent to sensuous experience, but his chief contribution to the theory of knowledge was his insistence on the importance of the general concept or definition.

It was Plato, however, who first realized the full significance of the problem and the necessity for coordinating the data of sense with the data of the intellect, he also first explained the origin of the problem. The universe of being, as reported by reason, is one, eternal, immutable; as revealed by sense, it is a series of multiple changing phenomena. Which is the truly real? For Plato there are in a sense two worlds, that of the intellect (noeton) and that of sense (horaton). Sense can give only an imperfect knowledge of its object, which he calls belief (pistis) or conjecture (eikasia). The faculties by which we apprehend the noeton, "the intelligible world" are two: nous, "intuitive reason", which reaches the ideas (see IDEA); and logos, "discursive reason", which by its proper process, viz. episteme "demonstration", attains only to dianoia "conception". Plato thus sets up two distinct intellectual faculties attaining to different sets of objects. But the world of ideas is for Plato the real world, that of sense is only a poor shadowy imitation. Aristotle's doctrine on the intellect in its main outline is clear. The soul is possessed of two orders of cognitive faculty, to aisthetikon, "sensuous cognition", and to dianoetikon "rational cognition" . The sensuous faculty includes aisthesis, sensuous perception", phantasia, "imagination", and mneme, memory". The faculty of rational cognition includes nous and dianoia. These, however, are not so much two faculties as two functions of the same power. They roughly correspond to intellect and ratiocinative reason. For intellect to operate, previous sense perception is required. The function of the intellect is to divest the object presented by sense of its material and individualizing conditions, and apprehend the universal and intelligible form embodied in the concrete physical reality. The outcome of the process is the generalization in the intellect of an intellectual form or representation of the intelligible being of the object (eidos, noeton). This act constitutes the intellect cognizant of the object in its universal nature. In this process intellect appears in a double character. On the one hand it exhibits itself as an active agent, in that it operates on the object presented by the sensuous faculty rendering it intelligible. On the other hand, as subject of the intellectual representation evolved, it manifests passivity, modifiability, and susceptibility to the reception of different forms. There is thus revealed in Aristotle's theory of intellectual cognition an active intellect (nous poietikos) and a passive intellect (nous pathetikos). But how these are to be conceived, and what precisely is the nature of the distinction and relation between them, is one of the most irritatingly obscure points in the whole of Aristotle's works. The locus classicus is his "De Anima", III, v, where the subject is briefly dealt with. As the active intellect actuates the passive, it bears to it a relation similar to that of form to matter in physical bodies. The active intellect "illuminates" the object of sense, rendering it intelligible somewhat as light renders colours visible. It is pure energy without any potentiality, and its activity is continuous. It is separate, immortal, and eternal. The passive intellect, on the other hand, receives the forms abstracted by the active intellect and ideally becomes the object. The whole passage is so obscure that commentators from the beginning are hopelessly divided as to Aristotle's own view on the nature of the nous poietikos. Theophrastus, who succeeded Aristotle as scholiarch of the Lyceum, accepted the twofold intellect, but was unable to explain it. The great commentator, Alexander of Aphrodisias, interprets the nous poietikos as the activity of the Divine intelligence. This view was adopted by many of the Arabian philosophers of the Middle Ages, who conceived it in a pantheistic sense. For many of them the active intellect is one universal reason illuminating all men. With Avicenna the passive intellect alone is individual. Averrhoës conceives both intellectus agens and intellectus possibilis as separate from the individual soul and as one in all men.

The Schoolmen generally controverted the Arabian theories. Albertus Magnus and St. Thomas interpret intellectus agens and possibilis as merely distinct faculties or powers of the individual soul. St. Thomas understands "separate" (choristos) and "pure" or "unmixed" (amiges) to signify that the intellect is distinct from matter and incorporeal. Interpreting Aristotle thus benevolently, and developing his doctrine Aquinas teaches that the function of the active intellect is an abstractive operation on the data supplied by the sensuous faculties to form the species intelligibiles in the intellectus possibilis. The intellectus possibilis thus actuated cognizes what is intelligible in the object. The act of cognition is the concept, or verbum mentale, by which is apprehended the universal nature or essence of the object prescinded from its individualizing conditions. The main features of the Aristotelean doctrine of intellect, and of its essential distinction from the faculty of sensuous cognition, were adhered to by the general body of the Schoolmen.

By the time we reach modern philosophy, especially in England, the radical distinction between the two orders of faculties begins to be lost sight of. Descartes, defending the spirituality of the soul; naturally supposes the intellect to be a spiritual faculty. Leibniz insists on both the spirituality and innate efficiency of the intellect. Whilst admitting the axiom, "Nihil est in intellectu quod non prius fuerit in sensu", he adds with much force, "nisi intellectus ipse", and urges spontaneity and innate activity as characteristics of the monad. From the break with Scholasticism, however, English philosophy drifted towards Sensationism and Materialism, subsequently influencing France and other countries in the same direction, as a consequence, the old conception of intellect as a spiritual faculty of the soul, and as a cognitive activity by which the universal, necessary, and immutable elements in knowledge are apprehended, was almost entirely lost. For Hobbes the mind is material, and all knowledge is ultimately sensuous. Locke's attack on innate ideas and intuitive knowledge, his reduction of various forms of intellectual cognition to complex amalgams of so called simple ideas originating in sense perception, and his representation of the mind as a passive tabula rasa, in spite of his allotting certain work to reflection and the discursive reason, paved the way for all modern Sensationism and Phenomenalism. Condillac, omitting Locke's "reflection", resolved all intellectual knowledge into Sensationism pure and simple. Hume, analysing all mental Products into sensuous impressions, vivid or faint, plus association due to custom, developed the sceptical consequences involved in Locke's defective treatment of the intellectual faculty, and carried philosophy back to the old conclusions of the Greek Sensationists and Sophists, but reinforced by a more subtile and acute psychology. All the main features of Hume's psychology have been adopted by the whole Associationist school in England, by Positivists abroad, and by materialistic scientists in so far as they have any philosophy or psychology at all. The essential distinction between intellect, or rational activity, and sense has in fact been completely lost sight of, and Scepticism and Agnosticism have logically followed. Kant recognized a distinction between sensation and the higher mental element, but, conceiving the latter in a different way from the old Aristotelean view, and looking on it as purely subjective, his system was developed into an idealism and scepticism differing in kind from that of Hume, but not very much more satisfactory. Still, the neo-Kantian and Hegelian movement, which developed in Great Britain during the last quarter of the nineteenth century has contributed much towards the reawakening of the recognition of the intellectual, or rational, element in all knowledge.

The common doctrine

The teaching of Aristotle on intellect, as developed by Albertus Magnus and St. Thomas, has become, as we have said, in its main features the common doctrine of Catholic philosophers. We shall state it in brief outline.

(1) Intellect is a cognitive faculty essentially different from sense and of a supra-organic order; that is, it is not exerted by, or intrinsically dependent on, a bodily organ, as sensation is. This proposition is proved by psychological analysis and study of the chief functions of intellect. These are conception, judgment, reasoning, reflection, and self-consciousness. All these activities involve elements essentially different from sensuous consciousness. In conception the mind forms universal ideas. These are different in kind from sensations and sensuous images. These latter are concrete and individual, truly representative of only one object, whilst the universal idea will apply with equal truth to any object of the class. The universal idea possesses a fixity and invariableness of nature, whilst the sensuous image changes from moment to moment. Thus the concept or universal idea of "gold", or "triangle", will with equal justice stand for any specimen, but the image represents truly only one individual. The sensuous faculty can be awakened to activity only by a stimulus which whatever it be, exists in a concrete, individualized form. In judgment the mind perceives the identity or discordance of two concepts. In reasoning it apprehends the logical nexus between conclusion and premises. In reflection and self-consciousness it turns back on itself in such a manner that there is perfect identity between the knowing subject and the object known. But all these forms of consciousness are incompatible with the notion of a sensuous faculty, or one exerted by means of a bodily organ. The Sensationist psychologists, from Berkeley onwards, were unanimous in maintaining that the mind cannot form universal or abstract ideas. This would be true were the intellect not a spiritual faculty essentially distinct from sense. The simple fact is that they invariably confounded the image of the imagination, which is individualized, with the concept, or idea, of the intellect. When we employ universal terms in any intelligible proposition the terms have a meaning. The thought by which that meaning is apprehended in the mind is a universal idea.

(2) In cognition we start from sensuous experience. The intellect presupposes sensation and operates on the materials supplied by the sensuous faculties. The beginning of consciousness with the infant is in sensation. This is at first felt, most probably, in a vague and indefinite form. But repetition of particular sensations and experience of other sensations contrasted with them render their apprehension more and more definite as time goes on. Groups of sensations of different senses are aroused by particular objects and become united by the force of contiguous association. The awakening of any one of the group calls up the images of the others. Sense perception is thus being perfected. At a certain stage in the process of development the higher power of intellect begins to be evoked into activity, at first feebly and dimly. In the beginning the intellectual apprehension, like the sensations which preceded, is extremely vague. Its first acts are probably the cognition of objects revealed through sensation under wide and indefinite ideas, such as "extended-thing", "moving-thing", "pressing-thing", and the like. It takes in objects as wholes, before discriminating their parts. Repetition and variation of sense-impressions stimulates and sharpens attention. Pleasure or pain evokes interest and the intellect concentrates on part of the sensuous experience, and the process of abstraction begins. Certain attributes are laid hold of, to the omission of others. Comparison and discrimination are also called into action, and the more accurate and perfect elaboration of concepts now proceeds rapidly. The notions of substance and accidents, of whole and parts, of permanent and changing, are evolved with increasing distinctness. Generalization follows quickly upon abstraction. When an attribute or an object has been singled out and recognized as a thing distinct from its surroundings, an act of reflection renders the mind aware of the object as capable of indefinite realization and multiplication in other circumstances, and we have now the formally reflex universal idea.

The further activity of the intellect is fundamentally the same in kind, comparing, identifying, or discriminating. The activity of ratiocination is merely reiteration of the judicial activity. The final stage in the elaboration of a concept is reached when it is embodied for further use in a general name. Words presuppose intellectual ideas, but register them and render them permanent. The intellect is also distinguished according to its functions, as speculative or practical. When pronouncing simply on the rational relations of ideas, it is called speculative; when considering harmony with action, it is termed practical. The faculty, however, is the same in both cases. The faculty of conscience is in fact merely the practical intellect, or the intellect passing judgment on the moral quality of actions. The intellect is essentially the faculty of truth and falsity, and in its judicial acts it at the same time affirms the union of subject and predicate and the agreement between its own representation and the objective reality. Intellect also exhibits itself in the higher form of memory when there is conscious recognition of identity between the present and the past. To the intellect is due also the conception of self and personal identity. The fundamental difficulty with the whole Sensationist school, from Hume to Mill, in regard to the recognition of personality, is due to their ignoring the true nature of the faculty of intellect. Were there no such higher rational faculty in the mind, then the mind could never be known as anything more than a series of mental states. It is the intellect which enables the mind to apprehend itself as a unity, or unitary being. The ideas of the infinite, of space, time, and causality are all similarly the product of intellectual activity, starting from the data presented by sense, and exercising a power of intuition, abstraction, identification, and discrimination. It is, accordingly, the absence of an adequate conception of intellect which has rendered the treatment of all these mental functions so defective in the English psychology of the last century.


About this page

APA citation. Maher, M. (1910). Intellect. In The Catholic Encyclopedia. New York: Robert Appleton Company.

MLA citation. Maher, Michael. "Intellect." The Catholic Encyclopedia. Vol. 8. New York: Robert Appleton Company, 1910. <>.

Transcription. This article was transcribed for New Advent by Tomas Hancil.

Ecclesiastical approbation. Nihil Obstat. October 1, 1910. Remy Lafort, S.T.D., Censor. Imprimatur. +John Cardinal Farley, Archbishop of New York.

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