ABSTRACT: The classical unresolved problem of the active intellect, raised by Aristotle in De Anima III.5, has received several interpretations in the history of philosophy. In this paper, I will recover the old hypotheses according to which the active intellect is the god of Aristotle's metaphysics. I propose that if the active intellect is god, it is not an efficient cause but the final cause of human thought-the entelecheia of the human rational soul. Nevertheless, the problem of the active intellect is insoluble simply because we do not count with all the elements required to obtain a sound solution. Yet it can be attenuated by an approach that renders much more coherence to De Anima III.5 than other attempts. To this end, I will (1) analyse the classical conception of Aristotle's two intellects, (2) work on the explanation par excellence of the active intellect, the metaphor of light, distinguishing the double conception of potency and act that may be found in it, and (3) analyse the concept of entelecheia as the process by which the active intellect actualizes intelligibles in the sense of the final cause.

One of the classic problems, and one of the most difficult to solve in Aristotelian philosophy, is that there is no text in which Aristotle explicitly states how the intellect manages to make 'intelligibles in actuality', that is, ideas. What he says in the fifth chapter of the third book of De Anima, instead of clarifying how man thinks, makes the intellectual process even more obscure, because the soul, as enteleceia of the body, is presented as one unit, but the mentioned text refers to two intellects, and one of them appears to be immortal, not human.

It is this intellect, precisely, which Aristotle describes as separate, immortal and eternal, characteristics attributed only to god. Based on such terms, critics have made numerous interpretations on the relationship between rational thought and god: whether man is (or has) the active intellect, whether he thinks together with god, or whether only god is the agent and man is a passive-potential intellect.

We think that the active intellect is, indeed, god, but that it is not 'really' an efficient cause of human thought, but rather the final cause or enteleceia of the human rational soul. Joseph Owens and W. Guthrie have recently affirmed this hypothesis. Traditionally, however, some other authors, even though they consider the active intellect to be a separate entity, have doubted or denied that it is god. Such authors are, inter alia: F. Nuyens, Ch. Lefèvre, J. Moreau and O. Hamelin. At the same time, certain affirmations link them to the group of authors that consider the intellect, although separate and a substance in itself, to be somehow united to the living being (man), as D. Ross affirms; the latter are the group who affirm today that the active intellect is in the soul while a man is alive.

In this article we seek to provide a reconstruction, using the elements at our disposal, of how intelligibles become actualized. For this purpose, we use here the metaphor of light that Aristotle himself uses to exemplify the active intellect in its work. It should be borne in mind that any solution to this problem can be no more than an approximation to what could have been Aristotelian thought, since we do not have sufficient elements to unravel the mystery completely.

I The theory of the two intellects

Traditionally one of these intellects was given the Aristotelian category of agent or active intellect; and, indeed, there is nothing strange about this, since in every movement there exists an agent and a patient, according to the treatises of Physics and Metaphysics. We should recall, however, that the agent is not only a being that acts physically on another, as an efficient cause: an agent (that which acts) is also the being that moves another by non-physical means, like the god of lambda book of Metaphysics moves the planets, namely, by desire.

The first objection made is to the very denomination of active intellect, because even though the expression nous paqhtikos is used at the end of the chapter, nowhere else in the chapternous poihtikos is explicitly mentioned; nevertheless, as Düring says, (1) the meaning is implicit when mention is made of the intellect that does everything,panta poiein, using the verb poiew, which refers to technical-productive actions and activity; that explains why the Latin term agens (from ago, agis agere: to do) is the one used, because it serves to designate the agent in physical movements. Nuyens explains that the origin of the term nous poihtikos is the joining of the phrase 'one (an intellect) that does everything' (o de to panta poiei) and the former phrase about the 'causal and active principle' (aition kai poihtikon).

It is in Aristotelian theory of thinking, borrowing the classical concepts of physical change, that we find the explanation of how the movement called intellecting comes about with all its elements; (3) the previous chapter (III.4) should be taken as an explanation of what the human intellect does when it apprehends (3) The first affirmation is the restatement of the equivalence between matter and potentiality, and form and actuality. This second term of the conceptual couple, however, is not mentioned as such: rather, the causal and active principle is mentioned. To these two functions or modi operandi, there correspond two intellects: the one 'that is capable of becoming all things' and the one that is 'capable of doing all things', which we will call, for the reasons given, patient and agent. The causal and active principle is that which makes it possible for universals to become actualized in the soul. Nuyens thinks that this is where Plato differs from Aristotle, (4) while for Plato universals exist already in themselves, for Aristotetle universals have to be actualized by the nous poihtikos, because they exist in things only in potentiality. (5)

This latter, since it can not act on the passive intellect, which is potentiality of the universals (and that would be the equivalent of the material principle if it were a common movement), is like a natural disposition, like light that 'somehow turns potential colors into actual colors'. Hence, it is not really an agent, since there is no acting in a natural process, and this is even more true if it is immaterial. That is why it is a natural disposition (exis).

This movement is analogous to perception, since it is a process of active states and of natural activity, that is conservation of what exists in potentiality by action of the entelecia. And if what potentially exists is the universal in the passive intellect, the action of understanding is produced by the active intellect that is an aentelecia, a natural disposition and not an 'agent' in the strict sense. What is this active intellect -entelecia - like?

'. . . And such intellect is separable, unmixed and impassive, being as it is actuality by its own entity' (6)

This coincides with the definition of intellect found in III.4. But:

What is meant by saying that it is actuality by its own entity?

Why, then, is there mention of this or that intellect?

One might think that two intellects are mentioned because of their different functions, but that they are functions of one and the same intellect. As for the agent, we can say that the agent is form, and as such it is entity, and it is in actuality. Form of what? Form is entelecia of something, and the intellect is not entelecia of anything (in the body), and it is not in actuality. Here it does not coincide with the concept of the intellect of man or of the rational soul. Therefore there is another intelligible principle here with new characteristics, different from those contemplated; in order to distinguish it, we must approach the comparison made by Aristotle in the metaphor of the light, and see how the habitual nature of the active intellect or agent is distinguished there.

II The metaphor of the light

At this point we should review the comparison made with perception using the example of the light (book II). In that part of De Anima we have some explanations (7) to which Aristotle alludes. There are three main elements in the explanation of vision: light, the transparent (diafanous) and the visible (orato), what one sees, which is color. The latter is the efficient cause of vision, it is what causes something to be seen. Indeed, all visible things have the (efficient) cause of their visibility, for they generate a physical movement.

'. . . The essence of color, in fact, consists of being the agent that sets the transparent into motion in actuality and the entelecia of the transparent is, in turn, light . . .' (8)

Therefore, there is a second element where the color of things is allowed to become manifest, for color itself could not be perceived over the sense. This element is the transparent, that which lacks color in itself, that is visible by virtue of the color of another thing, or in other words, that is the 'material' condition for that color to be seen. These elements are water, air, ether, etc. Now, with reference to the transparent:

The transparent is not visible by itself, but by color. There is a determined nature found in transparent elements.

The dark is the transparent in potentiality.

That implies that it is one same colorless nature that can be determined by light (visibility), color or darkness. And it is when the transparent is in actuality that it is possible for color to be seen, in a second actualization. This is because light is the entelecia of the transparent and it is what makes it possible, in the last instance (final cause). for things to be seen.

Here we must recall that there are two types of actuality. One (which will be second in the natural order) that results from the action of color: from the transparent we pass to the colored in actuality (energeia), which was potential in the transparent and was actualized by color. The other (which is the first one), light that is the entelecia of the transparent: whence light is a habitual disposition (9) that permits the actuality of the transparent. The entelecia normal light has the potentiality to make the transparent become in actuality.

Light is the actuality of the transparent while transparent (in potentially transparent bodies darkness exists), is its entelecia. Light is like the color (10) of the transparent when the transparent is in actuality under the action of fire or something similar. Light is not a body, nor is it the emanation of any body, but it is the presence of fire in the transparent. This implies that color is the efficient cause, the agent of the change, while Aristotle considers Light as the final form to which the transparent tends, or also, the natural principle that guides the movement of the transparent: entelecia. But it must be stressed that that is possible, in this case, because of a luminous body, such as fire or some similar nature: light, being part of a material process, has an efficient cause - fire. But, if color set the transparent in motion (second actualization), this is because the latter had that disposition thanks to light.

'Il faut donc, pour que la couleur mette en mouvement le diaphane, que celui-ci ait été préalablement actualisé par la lumière.' (11)

In a way, light turns potential colors into colors in actuality. Obviously the colors here are like actualized forms, the universals that existed potentially in the passive intellect (or in pure potentiality): this would be the transparent. We must not forget that there is a difference between the two processes because of the immaterial nature of the components. (12) The efficient and immediate cause of vision is not light but fire.

If light did not depend on anything material, it would not have an agent or an efficient cause such as fire; it would be an entelecia in itself, it would be act in itself and would be the first cause in itself, which causes the first movement: the actualization of the transparent. Likewise, if what is transparent and colored were something immaterial, it would have the transparent-to-light as final cause, as entelecia, but it would not have an efficient cause (color) since there would be no agent to act on it physically. For that, the transparent would not be a body like air, water or something similar. Color would become actualized impassively in the pure potentiality of the transparent, as long as there be light.

However, at this point we must be sure that we understand, as we already mentioned when discussing the soul, that light is an entelecia: it is an already completed act (unlike the energeia. (13) ); therefore light is an agent, and for that reason it informs (already identified by Aristotle with entelecia). Thus, similarly, the intellect is the 'pure intelligible form already separated; this form would evoke, would call to itself, so to speak, the forms enclosed in imaginative matter'. (14) Hamelin apparently saw in the active intellect a final cause whereby the ideas become actualized in a natural process in the passive intellect.

Guthrie contends that the external efficient cause of thought, that is the active intellect, is the first cause of the movement of all nature, that is god or the primary mover. (15) To reach this conclusion, he has also placed emphasis on the metaphor of light, and its third element role that makes the act of vision possible, together with sight and the object. (16) Guthrie is convinced that:

'. . . The First Cause is common to all (the four causes), although at the same time it is the cause of development in the bosom of the individuals of each species. Thus, in De Anima, leaning on the interpretation offered here, Aristotle is saying that 'exactly the same as in nature, thus also in the soul', the First Cause calls to activity the latent human thoughts.' (17)

Guthrie believes, too, that the parallelism that Aristotle 'invites us to trace' between the physical and the psychic world is the most important reason for considering the active intellect as the primary mover. (18)

'. . . Evidently his objective was to unify the whole cosmic system by making God, the Primary Unmoved Mover and (let us not forget this) the supreme nous, the final cause of all kind of change.' (19)

It should be emphasized that in Guthrie's opinion the active intellect calls latent human thoughts into activity; and Hamelin is of the same opinion. Hamelin says that the intellect evokes, or calls to itself the forms enclosed in imaginative matter. (20) In both cases, the active intellect of the final cause function is clear (as opposed to a typical efficient cause, as many scholars have thought).

Owens, who believes that the active intellect works as final cause and is god, considers that the example of the light is one of the principles for an understanding of the fifth chapter, since Aristotle conceives light as actuality (energeia) and as a positive state (exews) that by its mere presence makes colors visible. (21)

'. . . Light actualizes colors by its mere presence. The comparison does not communicate the notion of doing something in the line of efficient causation. The light is simply there, and when it is there the different colors are visible. The comparison would mean that while the active intellect is there, that is by its very ousia, perceivable things become intelligible, just as in the light of day colors are visible.' (22)

We were saying that in a way the active intellect turns the potential universals (or forms or entelecias of things) into universals in actuality. But the active intellect is actuality, entelecia, like light: light makes colors possible, just as the active intellect makes universals possible. They both require 'something' to potentially be and able to become actualized: for light, we have the matter (second) that is transparent and that in its state in potentiality is darkness, and without light it is transparent in potentiality (the colorless is 'nothing', from the visual point of view before the light).

Analogously, for the active intellect, which is immaterial and pure actuality, form and entelecia in itself, we have as correlation the passive intellect or the intellect with which the soul thinks, which is also immaterial and which, without the agent (in other words, in the state of potentiality) is 'nothing before understanding', (23) and can be any thinkable form.

'. . . Every perceivable object is, therefore, capable of becoming understood through that intelligible light. In the same way, the active intellect can be valued as the instrument of human knowledge. It makes perceivable objects intelligible. As supremely intelligible it functions, consequently, as the final cause of human aprehension.. .' (24)

What happens when one understands? The intellect in actuality identifies with its objects (transparency and color are the same thing when the transparency is in actuality, because its actuality is color and its entelecia is light or visibility). This metaphor of the light is, evidently, one that clarifies the activity of the active intellect that can not be a common agent (physical), since we are dealing with an immaterial process.

III The active intellect as entelecia

Who actualizes the universal? Aristotle did not state clearly whether it is man himself or an external principle. But the 'formulas that he uses' suggest that the second hypothesis is true. (25) Owens notes here that the immateriality of the form resulting from perception makes the process different:

'But while in the material reception the form causes a third thing to arise, namely the product, its immaterial mode of reception has a very different result. It makes the perceiver and the perceived object, the knower and the known object, identical in the actuality of the knowledge. No third thing arises, but rather there is merely a complete identity of both in cognitional being. . .' (26)

This implies that there is no efficient cause for thought, and that when one understands the universal of an image, the movement made is one of natural activity, of realization of the nature of the intellect. It is not an accident, neither is any change or action performed when one is understanding: the human intellect, impassible, contemplates or takes in the universals of the bodies by means of images and it actualizes them, identifying itself with them, because it is pure potentiality of all things, of any universal, of any form. Barbotin contends that (27) this intellect can be called passive only in relation to the active principle; besides:

'L'identité potencielle de l'intellect avec toutes les choses est l'élément commun qui rend possible la passion.' (28)

Obviously, passion without action. Guthrie thinks that Aristotle did not make the separation explicit because he himself found it a problem to explain how the process of understanding is performed, (29) and when he could no longer avoid the issue, he applied his physical principles, even though here we would be dealing with a special, different process. At the same time, he points out that, if the intellect is pure potentiality (and this is equivalent in terminology to matter), it would be, in the scale of beings, lower down than the body (lower than composite substance), and this anomaly must be clarified, because in fact the intellect has to be higher on the scale. (30) That leads him to propose the analysis of the active/passive duality within the intellect itself only after chapter III.4. For Owens, the objection is resolved in the metaphor of the light and his explanation in De Anima:

'. . . The context in which the passage is situated, i.e., taking form to matter in the natural universe, appears to demand an explanation in terms of efficient causality. But in the same way that Aristotle was able to accept the fact of the physical universe in its entirety without concluding that there was a creative cause, he is also able to consent to the fact of intelligibility without inferring an attached efficient cause . . . Aristotle can recognize the presence of the visible world without worrying about the creative cause. Why, then, could he not see intelligibility as a fact and illustrate it using the metaphor of light, even when an efficient cause is not inferred? The full context appears to demand an efficient cause, and yet the Aristotelian problem with the perfection of the efficient causality localized outside, in the passum, would prevent it from being considered.' (31)

If this is correct, our interpretation is going in the right direction. We must bear in mind that all the language used by Aristotle for the intellective process is, then, analogous to, and borrowed from, that of normal physical processes: there is not a real potentiality, since there is not a 'material' intellect with potential universals (whereas there is an informed human body that has organs by means of which the soul captures in the perceivable in potentiality); neither is there an efficient agent-cause, but rather an entelecia that serves as agent final-cause for the intellective process.

Perhaps the relationship that seems so difficult to us to accept today, namely that this active principle of thought is god and that it can not be otherwise, was such an evident truth that even Aristotle did not bother to explain it.

' . . .Now, it is impossible for there to be anything better or higher than the soul, and it is even more impossible for there to be nothing better or higher than the intellect. It is, of course, absolutely reasonable that the latter be the original and sovereign by nature . . .' (32)

Obviously, he is referring to the divine intellect, the unmovable mover who governs all nature, and according to our interpretation, all psychic processes. It is no accident that both Theofrastes and Eudemes, disciples of Aristotle, have affirmed that the intellect is divine, that it comes from outside, and even (Eudemes), explicitly, that it is god. (33) Although all the evidence we have found in this reference leads us to believe that it was so, Aristotle has left us not one written word that really states, explicitly, that the active intellect is god, and that for that reason it is as it is. As we said at the beginning, this is a problem that has no final solution.


(1) Düring, Ingemar, Aristóteles, Mexico: UNAM, 1990, P.899.

(2) Cf.Guthrie, W.K.C., Historia de la Filosofía Griega, Madrid: Gredos, 1993, six volumes, (translated by Alberto Medina González), volume VI.

(3) Nuyens says that the fouth chapter explains how man apprehends, and the fifth presents the explanation of the active principle that makes intelligibles in actuality.

(4) Nuyens, F., L'Evolution de la Psychologie d'Aristote, Louvaine: Editions de L'Institut Supérieur de Philosophie, 1973, p.297.

(5) Obviously, we are dealing here with the universals that make possible the knowledge of things, that is, the intelligibles or separate forms, since things are informed by the universals or essences, that is, they exist in them.

(6) De Anima 430a17.Aristóteles, Acerca del Alma, Madrid: Gredos, 1983 (Introduction, translation and notes: Tomás Calvo Martínez).

(7) De Anima 418b and ff. We will refer henceforth to the seventh chapter of the second book.

(8) De Anima 419a 10-12.

(9) We will see later what is meant by saying that the intellect is a natural disposition (ezis) like light.

(10) This is an illustrative comparision, not its true essence.

(11) (So in order for color to set in motion the transparent, the latter must necessarily have been previously actualized by light.). Barbotin: Aristoteles, De L'Ame, Paris: Les Belles Lettres, 1989, 13th edition (Translation and notes by E. Barbotin), p.49 n.4.

(12) This will imply certain special characteristics in the efficient cause and the potentiality.

(13) Although entelecia coincides with form, Aristotle refers to entelecia as the final perfection of a form. Henri Carteron, in note #2 on p.90 of Physics cites Bonitz (Index) 253b35: 'D'ordinaire l'acte (entelecia) est ce qui conduit a l'essence parfaite, l'entéléchie est l'essence parfaite elle-même.'. See García Yebra, n.11, p.246, in his edition of Metaphysics, Madrid: Gredos, 1987 (trilingual edition by Valentín García Yebra): ' . . . entelecia is not simply the act, but the completed act, that has reached its natural perfection.'. See also Metaphysics 1050a22-24: '. . .The work is an end and the act (entelecia) is the work; for that reason also the word act is directly related to work and tends toward entelecia)'.

(14) Hamelin,O., El sistema de Aristóteles, Buenos Aires:Estuario, 1946, p.453.

(15) Guthrie, op.cit. p.331 ff.

(16) That is, together with the patient and the agent of vision.

(17) Ibid. p.336.

(18) Ibid. p.335.

(19) Ibid. p.336.

(20) See note 12.

(21) Owens, J., 'El Problema de la Causación del Intelecto Agente en el De Anima (3.5) de Aristóteles' ['The Problem of the Causation of the Active Intellect in Aristotle's De Anima (3.5)] in: Revista de Filosofía, Mexico: Universidad Iberoamericana (Departamento de Filosofía), Sept-Dec., 1990, No.69 pp.409-417, (Translated by Ma.Teresa de la Garza)., p.412.

(22) Ibid., p.414.

(23) De Anima 429b30 ff

(24) Owens, J., op.cit., pp. 415-416.

(25) Ibid. pp. 295-296.

(26) Owens, J., op.cit., p.411.

(27) Barbotin, op.cit., p. 82n. 5.

(28) (The potential identity of this intellect with all things is the commun element that makes passion possible.). Ibid., p.81 n.7.

(29) Guthrie, W.K.C., op.cit., pp. 328-329.

(30) Ibid., pp.330 ff.

(31) Owens, J., op.cit., p.414.

(32) De Anima 410b12-15

(33) Cf. Hamelin, O., La théorie de l'intellect d'après Aristote et ses commentateurs, Paris: Libraire Philosophique J. Vrin, 1948, pp.29-31. We are not talking here of authors influenced by the neo-Platonics or the Academics, but of purely Peripathetic philosophers. We have referred to these authors only because they were immediate disciples of Aristotle.