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Home > Catholic Encyclopedia > S > Species


In scholastic terminology, Species is the necessary determinant of every cognitive process. Few scholastic doctrines have been more frequently misunderstood, misrepresented, and ridiculed than that of the species intentionales. And yet few are more obvious and unobjectionable, although we are no longer accustomed to them. While using different terms, modern psychology offers an explanation of knowledge which, in its essential features, is identical with that which was proposed by the great thinkers of the Middle Ages.

Knowledge is essentially the union of an object with the mind. As the cognitive process takes place in the mind, it follows that the known object must in some manner be present in the mind. "Cognitio contingit secundum quod cognitum est in cognoscente" (St. Thomas, "Contra gentiles", II, c. lxxvii and xcviii). Any cognitive faculty is indetermined, or in potentia in two ways:

Thus the eye can perceive any colour; the ear, any sound; the intellect, any conceptual relation, etc. To pass from this state of twofold indetermination to a concrete and determined act of knowledge, the faculty needs a complement, a determining principle, or actus (see ACTUS ET POTENTIA). It must be "informed", or acted upon, by its object. For this reason all faculties of knowledge were called passive, not in the sense that the mind is merely passive in its cognitive process, but in the sense that it must first be acted upon, and thence be enabled to exercise its own cognitive activity. In other words, knowledge is not a spontaneous activity springing from the mind alone, but a reaction in response to an external stimulation.

The "species", frequently also called forma, is the determinant of the mind in the process of knowledge. It partakes of the nature both of the object from which it proceeds, and of the faculty in which it is received, for, as the scholastic axiom expresses is: "Quidquid recipitur per modum recipientis recipitur." And more specifically: "Cognitum. est in cognoscente secundum modum cognoscentis" (St. Thomas "Summa theol.", I, Q. xii, art. 4). Hence the species impressa is the modification of the faculty by the action of the object. The species expressa is the reaction of the mind as a cognitive process. The former is impressed in the faculty which it determines, and corresponds to the passive phase of knowledge which is a necessary condition but is not yet actual knowledge. The latter is the active response of the faculty, the cognitive process itself by which the mind reaches the object. The species must not be conceived as a substitute for the object, but as a mere medium of knowledge. The mind reaches the object directly and immediately, not the species. The species is not that which is known, "id quod cognoscitur", but that by which the object is known, "id quo objectum cognoscitur" (St. Thomas, "Summa theol.", I, Q. xii, art. 9; Q. xiv, art. 5; Q. lxxxv, art. 2; "De Veritate", Q. x, art. 8, ad 2um, etc.). The object as acting on the faculty, and the faculty as acted on by the object, are one and the same reality. Actio and passio are the same thing with two aspects or phases. Hence there is no need of a bridge to pass from the subject to the object. The question: how can the mind know extramental objects? has no meaning when knowledge is conceived as the vital union of the known object with the knowing mind.

This general function of the species applies to both sensitive or organic and intellectual or spiritual faculties of knowledge. The species sensibilis is not an efflux from the object, not a physical miniature of it — a view which was accepted by some interpreters of Aristotle, but which the great scholastics, with St. Thomas, reject. It is a modification of the sense organ by the action of the object. It is sometimes called material because it results from the activity of material objects, and is a modification of a material organ. Sometimes also it is called intentional, or even spiritual, because it is not in itself a material representation, and is not received in physical matter, but in an organ which is animated by the soul. In other words, it is psychophysical. The species intelligibilis is the determinant of the intellectual act of knowledge. It is elaborated from the data of the senses by a special activity of the intellect (intellectus agens), and received in the intellectus patiens or possibilis which elicits the act itself of knowledge (see INTELLECT).


BOURQUARD, Doctrine de la connaissance d'aprés St. Thomas d'Aquin. (Paris, 1877); KLEUTGEN, Die Philosophie der Vorzeit (Münster, 1867); LIBERATORE, Della conoscenza intellettuale (Rome, 1873); MARER, Psycholoqy (New York and London, 1910);. PESCH, Institutiones psychologicæ (Freiburg, 1897); TURNER, History of Philosophy (Boston, 1903), 363.

About this page

APA citation. Dubray, C. (1912). Species. In The Catholic Encyclopedia. New York: Robert Appleton Company.

MLA citation. Dubray, Charles. "Species." The Catholic Encyclopedia. Vol. 14. New York: Robert Appleton Company, 1912. <>.

Transcription. This article was transcribed for New Advent by Douglas J. Potter. Dedicated to the Sacred Heart of Jesus Christ.

Ecclesiastical approbation. Nihil Obstat. July 1, 1912. Remy Lafort, S.T.D., Censor. Imprimatur. +John Cardinal Farley, Archbishop of New York.

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