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Is there one intellect for all men, or does each man have his own intellect? This problem involves two questions often discussed by Christians of the Middle Ages:(1) Is the agent intellect one for all men? (2) Is the possible intellect, as well as the agent intellect, one for all men? (see intellect.) Of the two questions, the second presented the more serious difficulty and was the subject of a vigorous polemic in the 13th century. The meaning and implications of both questions can best be understood in the light of their historical background.

History of the problem . The story begins with Aristotle's De anima. Noting that in nature as a whole we find

two factors, a potential factor and an active one, aristot le says that "these distinct elements must likewise be found within the soul" (430a, 13). He then continues:

And in fact mind as we have described it is what it is by virtue of becoming all things, while there is another which is what it is by virtue of making all things. Mind in this sense is separable, impassible, unmixed, since it is in its essential nature activity. When mind is set free from itspresent conditions it appears as just what it is and nothing more; this alone, is immortal and eternal. While mind in this sense is impassible, mind as passive is destructible, and without it nothing thinks. [430a, 1425.]

The fact that Aristotle distinguished an active intellect that makes things actually intelligible from a passive intellect that receives these intelligibles was clear, but precisely what he held about the natures of these intellects and their relationship to man was not. Although these words were to be examined and reexamined and compared with other of his statements, commentators could not agree on what he really meant. The reference to active mind as separable, impassible, unmixed, immortal and eternal, for example, gave rise to the question: Is active mind a power of the human soul or a substance separate and distinct from man?

Among the Greek commentators, Theophrastus (c. 370285 b.c.) and Themistius (c. a.d. 387) interpreted Aristotle as holding that both active and passive intellects were parts or powers of each human soul. But Alexander of Aphrodisias (c. a.d. 200), though placing the passive or material intellect within the individual soul, which was for him perishable, taught that the active intellect is a separately existing divine intelligence.

Among Arabian thinkers, too, the active or agent intellect was held to be a separated substance and one for all men. For avicenna (9801037), the last of the separate spiritual intelligences emanating from the one necessary Being was the agent intellect or Intelligence (Meta. 9.4). From this intellect, intelligible forms or species were infused into possible intellects belonging to individual human souls. Each human soul had to consider and compare the images coming to it from the senses. These movements prepared it to receive from the separated agent intellect an "abstraction," which in this context meant an emanation of intelligible forms. But the intelligibles so received were not retained. Each time a man wished to have intellectual knowledge, his soul again had to be united with the separate agent intellect (De anima 5.56).

For Avicenna, although there was one agent intellect for all men, each man had his own possible intellect. But for averroËs (112698), the individual man had neither; the possible as well as the agent intellect was a separated substance and one for all men. Reacting against the materialism of Alexander of Aphrodisias, Averroës held that the possible or "material" intellect must be a simple, impassible, separated substance dwelling wholly apart from matter. This was necessary to insure its power of knowing universals (In 3 anim. comm. 4,5,19,32). But since this view left the individual without a spiritual intellect, Averroës still had to explain how man can have intellectual knowledge. Therefore man's highest powers, the cogitative power, imagination, and memory, were given the task of preparing sensory data for the separated intellects to utilize (ibid., comm. 6,20,33). The separated agent intellect then makes actually intelligible the intelligible species potentially present within the phantasms provided by these powers. The separated possible intellect can thereupon be actuated and become the subject in which knowledge exists (ibid., comm. 4,5,18). Unless such data were provided by man, the separated possible intellect would know nothing (ibid., comm. 33). Because of man's indispensable role in this process, he himself somehow shares in intellectual knowledge.

This may not completely explain how the individual man knows. But Averroës could not concede that the intellect was "numbered to the number of individuals," and still have that intellect sufficiently free of matter to preserve its power of knowing. He had no awareness of a spiritual intellective soul that could be the form of a body without being itself immersed in matter (see soul, human).

Christian thought . These views that gradually became known to the Christians of western Europe as the works of Aristotle, accompanied by commentaries of Arabian thinkers, became available in Latin translation during the 12th and 13th centuries. While Aristotle's logical works had previously been known and admired, Christians now had access to his other treatises, including that on the soul. Avicenna's De anima and Averroës' Commentary were also available as aids in understanding his complex thought.

This new literature was viewed by some authorities as a possible source of error. In 1210 the provincial council of Paris prohibited the teaching of Aristotle's works on natural philosophy or their commentaries. In 1215 the statutes of the University of Paris promulgated by robert of courÇon, the papal legate, forbade the reading of the physical and metaphysical treatises of Aristotle and expositions based on them (Chartularium universitatis Parisiensis, 1:70, 7879). But the prohibitions were not effective.

Avicenna's doctrine of a separated agent intellect had already been accepted, in a modified form, by a 12th century Christian, dominic gundisalvi. He, roger bacon (b. c. 1214) and john peckham (d. 1292) all identified this agent intelligence with the Christian God. Étienne Gilson has seen in the work of these and others a fusion of the Avicennian doctrine on the agent intellect with an Augustinian doctrine of illumination (Gilson, "Pourquoi saint Thomas a critiqué saint Augustin," Archives d'histoire doctrinale et littéraire du moyen-âge, 1:5127).

The unity of the agent intellect in the human species met further opposition in the 13th century. Along with the unity of the possible intellect, it was included in the condemnation of 1270 whereby Étienne tempier, Bishop of Paris, anathematized 13 propositions bearing the stamp of Arabian authorship, and again in the list of 219 propositions condemned in 1277 (Chartularium universitatis Parisiensis, 1:486487, 543548).

It was also opposed in the writings of St. thomas aquinas (122574). According to St. Thomas, Aristotle taught that the agent intellect was not a separate substance but a power of the human soul with the function of making the potentially intelligible natures of sensible things actually intelligible, by abstracting them from individual matter (C. gent. 2.78). This view is confirmed, for St. Thomas, by man's experience in abstracting universal forms from their particular conditions. If the power that is the principle of this action were not something within man's soul, human nature would be a deficient nature, lacking the principle of an activity proper to it (C. gent. 2.76; ST 1a, 79.4; In 2 sent. 17.2.1; De anim. 5; In 3 de anim. 10.734). Wishing to save the efficacy of secondary causes, St. Thomas held that a being cannot be incapable of accomplishing an operation proper to its nature. Yet this need not rule out the dependence of man's intellectual soul upon a higher cause. "The separate intellect, according to the teaching of our faith, is God Himself. Therefore the human soul derives its intellectual light from Him," St. Thomas said. He went on: "That true light illumines as a universal cause, from which the human soul derives a particular power" (ST 1a, 79.4 and ad 1). There may then be some reason for holding that there is one agent intellect for all men, when this is understood not as a denial but as an explanation of the personal agent intellect that each man possesses. But, in St. Thomas's view, to say that the possible intellect is one for all men is wholly inadmissible (De anim. 5; De unit. intell. 4).

Before the emergence of a definite Averroistic school, St. albert the great (c. 120080) had already dealt with this doctrine at the request of Pope Alexander IV. In 1256, in his De unitate intellectus contra Averroem, he presented 30 arguments for the unity of the human intellect and 36 arguments against it.

But the Averroist movement grew in strength (see averroism, latin). As more Christian thinkers read Aristotle and Averroës in Latin translation, the Philosopher and philosophy were seen through the works of the Commentator. These Latin Averroists regarded the doctrine of one possible intellect for all men as a necessary conclusion of human reason, although as Christians they refrained from saying that this doctrine was true. Without explicitly teaching a theory of double truth, such a leading Averroist as siger of brabant (fl. 1277) nevertheless conveyed the impression of a conflict between faith and reason. For those concerned with the unity of Christian wisdom, this challenge could not be ignored (see dou ble truth, theory of).

St. bonaventure (122174) referred to the doctrine of one possible intellect for the whole human race as being against the Christian religion, against right reason and against sensible experience (In 2 sent. 18.2.1). The same doctrine was censured in the condemnations of 1270 and 1277. It was listed as an error by giles of rome (c. 12471316, Errores philosophorum, c.4) and opposed in a treatise he wrote on the problem (De plurificatione intellectus possibilis ).

Thomistic doctrine . The most thorough philosophical examination and refutation of the Averroist doctrine of the possible intellect was made by St. Thomas Aquinas. He discussed it in many places and composed the polemical treatise, De unitate intellectus contra Averroistas, specifically to deal with this problem. Written in 1270 against the Paris Averroists and especially against Siger of Brabant, it may have been an answer to a work of Siger's that is no longer extant but is known to us through the Quodlibeta of john baconthorp, a 14th century Carmelite.

St. Thomas regards it as evident that Averroës' view of one possible and one agent intellect for all men is contrary to the truth of Christian faith. Since this would leave man without any incorruptible part of the soul, there could be no personal immortality and thus no reward and punishment in the afterlife. He concentrates on showing that the position of the Averroists is against both Aristotle and sound philosophy. On neither ground can they maintain that the possible intellect is (1) a substance separate in its being from man, or (2) one for all men (De unit. intell. proem.).

St. Thomas analyzes the relevant and often ambiguous texts of Aristotle and also cites the Greek and Arabian peripatetics, to show that all support the view that each man has his own possible intellect. His arguments include stress on the fact that "this individual man knows" and that Averroës' doctrine, which treats man as an object of knowledge for the separated possible intellect, fails to explain this. Man's proper operation as man is to understand. Therefore the principle that gives him his specific nature, the principle by which he understands, must be his own and not a separated substance (ibid. 3).

St. Thomas also deals with the chief difficulty of the Averroists. They thought that if the intellect is a power of a soul that is itself the substantial form of a body, then it would become immersed in matter and so be incapable of intellectual knowledge. St. Thomas answered that a proper understanding of the relation of the human soul to the matter it informs removes this difficulty. The human soul is not a material form existing with only the being of the composite; rather, it exists with its own being, and through that being the composite exists. Since this form is a substance communicating its being to matter, nothing prevents it from having an immaterial operation or power (ibid. 1.3).

For St. Thomas this error on the intellect pointed to an even greater error on the relation of faith and reason (see faith and reason). He was deeply disturbed that anyone could say: "By reason I necessarily conclude that the intellect is one in number, but I firmly hold the opposite by faith." Such a person, Siger for example, seemed to imply that faith is concerned with what is false and impossible (ibid. 5). Departing from his usual dispassionate style, St. Thomas concludes his treatise with a challenge to his adversary: "Let him not speak in corners nor before boys who do not know how to judge of such difficult matters, but let him write an answer to this if he dares. He will find not only me, least of all, but many others who are zealous for truth, through whom his error may be resisted or his ignorance remedied" (ibid. 5).

Because of the difficulty of establishing the authenticity and chronology of writings attributed to Siger of Brabant, it cannot be said for certain that this challenge was accepted by Siger. He may have replied in De intellectu, a treatise mentioned by john of jandun (d. 1328) and Agostino nifo (1473c. 1538). His De anima intellectiva seems to reflect a knowledge of some of St. Thomas's comments, and its doctrine of the intellective soul as united to the body "intrinsically" for its operation may represent a change or clarification of an earlier position (De anim. intell. 3). But unless the authenticity of such a work as the Quaestiones in libros Aristotelis de anima can be established, it cannot be said that Siger was converted to a Thomistic position.

The controversy over the intellect was to continue into the 16th century. Pietro pomponazzi (d. 1525), like John of Jandun before him, did not doubt that St. Thomas's conclusions were in agreement with faith, but could not see them as philosophical conclusions in accord with Aristotle's position. Those who identified philosophy with the historical Aristotle were thus reluctant to accept an Aristotle transformed by the creative insight of St. Thomas. Yet, regardless of such interpretations, there is no dearth of philosophical argument in support of the conclusion that each man has his own possible, as well as his own agent, intellect.

See Also: aristotelianism; scholasticism; thomism; arabian philosophy; abstraction; illumination; neoplatonism.

Bibliography: e. gilson, History of Christian Philosophy, 181225, 387410. f. van steenberghen, Aristotle in the West, tr., l. johnston (Louvain 1955). p. f. mandonnet, Siger de Brabant et L'averroisme latin au XIII e siècle, 2 v. (2d ed. Louvain 190811). É. h. gilson, "Les Sources gréco-arabes de l'Augustinisme avicennisant," Archives d'histoire doctrinale et littéraire du moyen-âge, 4 (192930) 5149. Chartularium universitatis Parisiensis, ed., d. denifle and e. chatelain, 4 v. (Paris 188997).

[b. h. zedler]

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Intellect, Unity of

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