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The Great Thinkers of Western Philosophy |
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IV. Theory of Knowledge (Epistemology) To explain the process of knowledge, Thomas Aquinas has recourse neither to the innate ideas of Platonism nor to the illumination of Augustine. Instead, he postulates a cognitive faculty naturally capable of acquiring knowledge of the object, in proportion to that faculty. Agreeing with Aristotle, he admits that knowledge is obtained through two stages of operation, sensitive and intellective, which are intimately related to one another. The proper object of the sensitive faculty is the particular thing, the individual; the proper object of the intellect is the universal, the idea, the intelligible. But the intellect does not attain any idea unless the material for that idea is presented to it by the senses: "Nihil est in intellectu quod prius non fuerit in sensu." The two cognitive faculties, sense and intellect, are naturally capable of acquiring knowledge of their proper object, since both are in potency -- the sense, toward the individual form; and the intellect, toward the form of the universal. The obtaining of the universal presupposes that the sensible knowledge of the object which lies outside us comes through the impression of the form of the object upon the sensitive faculty. This is likened to the impression of the seal upon wax. Upon this material impression the soul reacts according to its nature, that is, psychically, producing knowledge of that particular object whose form had been impressed upon the senses. Thus the faculty which was in potency is actuated with relation to that object, and knows and expresses within itself knowledge of that particular object. But how is the passage made from sensitive cognition to that which is intellective? Or, rather, how is the individual form which is now offered by sensible cognition condensed into an idea and thus made the proportionate object of the intellect? To understand the solution to the problem, it is necessary to recall the theory of Aristotle which Aquinas makes his own; that is, that the individual form is universal in potentia. It is the matter which makes the form individual. Hence if the form can be liberated from the individualizing matter, or dematerialized, it assumes the character of universality. According to Thomas Aquinas, this is just what happens through the action of a special power of the intellect, i.e., the power by which the phantasm (sense image) is illuminated. Under the influence of this illumination, the form loses its materiality; that is, it becomes the essence or intelligible species (species intelligibilis). Thomas call this faculty the intellectus agens (agent intellect), and it is to be noted that for Thomas the "intellectus agens" is not, as the Averroists held, a separate intellect which is common to all men. For Aquinas, the agent intellect is a special activity of the cognitive soul, and it is individual and immanent in every intellective soul. The "species intelligibilis" is then received by the intellect, which is called passive since it receives its proper object, and become intelligible in act. Note that according to Aquinas the form, both intelligible and individual, is not that which the mind grasps or understands (this would reduce knowledge to mere phenomenalism), but is the means through which the mind understands the object (individual form) and the essence of the object ("forma intelligibilis"). Knowledge thus has its foundation in reality, in the metaphysical. Furthermore, since the cognitive faculty is in potency, when it becomes actuated, it becomes one with the form which actuates. Thus it may be said, in a certain sense, that the intellect is identified with the determined form which it knows. For Aquinas all the data of sense knowledge and all intelligible things are essentially true. Truth consists in the equality of the intellect with its object, and such concordance is always found, both in sensitive cognition and in the idea. Error may exist in the judgment, since it can happen that a predicate may be attributed to a subject to which it does not really belong. Besides the faculty of judgment, Aquinas also admits the faculty of discursive reasoning, which consists in the derivation of the knowledge of particulars from the universal. Deductive, syllogistic demonstration must be carried out according to the logical relationships which exist between two judgments. In this process consists the science which the human intellect can construct by itself, without recourse either to innate ideas or to any particular illumination.
Aquinas accepts the general principles of the metaphysics of Aristotle, for whom there are two principles of being, potency and act. Act signifies being, reality, perfection; potency is non-being, non-reality, imperfection. Potency does not, however, mean absolute non-being, but rather the capacity to receive some perfection, the capacity to exist, as Aristotle taught. The transition from potential to actual existence is becoming, that is, the passage from potency to act. Outside of becoming there exists Pure Act, the absolute reality and perfection upon which all becoming depends. The general principle of metaphysics, potency and act, applied to that part of becoming in which matter is already existent, is specified in a second principle, the principle of matter and form. Matter which in potency is not be understood as pure nothingness, but is as a being having in itself no determination. Thus matter is to be conceived of as the substratum of form. The form which is in act gives to the matter specific determination, reality, perfection -- that which we mean when we ask what is such and such a thing. The union of matter and form constitutes or gives place to the substance, to the "totum," the individual. Relative to the question of the principle of individuation, or the question of how it happens that a determined specific form can give place to a multiplicity of individuals of the same species, Aquinas affirms that the principle of individuation is matter -- not matter considered abstractly, pure matter, but matter signed by quantity, or that concrete matter in which the new form is produced. If prime matter and substantial form are sufficient to constitute the "totum" (the substance), then this latter, to be perfect, can and must receive other or secondary forms, i.e., accidental forms which give new determination to the substance (quantity, quality, etc.). The accidents, since they are determinations of the substance, are ordained to the substance and depend on it. The concept of matter and form gives us an explanation of how a thing becomes, but does not tell why it becomes. To present us with the why of becoming, it is necessary to have recourse to a third concept -- that of efficient cause -- which produces such a determination of form in matter and is the reason why this particular form arises in the matter. Finally, to give us the reason why the efficient or acting cause or agent is made to bring about the union of this form in this matter, we need a fourth element, the concept of end. End (finis) indicates the purpose the agent has in mind when he acts, or gives actuation to this form in this matter. Final cause hence indicates the end, and also the order according to which the agent is determined to act: First in intention, the purpose or end is last in execution -- the purpose of the agent is achieved only when the entity is completed in its material element and its substantial and accidental forms. Thus for Aquinas, as for Aristotle, the concepts explaining reality are reduced to the concepts of the four causes -- material, formal, efficient, and final.
VI. The Existence of God (Theodicy) The Five Ways The search for God and His relationship with the world was as fundamental in the Middle Ages as it was at any time during the history of Christian thought. At the time of Aquinas, Augustinianism was the most appreciated doctrine in the school of philosophy at the University of Paris. In virtue of illumination, which is the central point of Augustinianism, the human soul could have an intuitive knowledge of God. Indeed the intellect had only to reflect upon itself to find the presence of the Divine Teacher. Thus the existence of God was proved a priori by means of necessary reason. Obviously, if the presence of the ideas of absolute truth and good in our mind must be explained by the direct suggestion of God, we do not need any other proof of God's existence. But, according to Aquinas, any natural intuitive knowledge of God is precluded to man. For us, only the visible world, which is capable of impressing our senses, is the object of natural intuitive knowledge. Thus any argument a priori for the existence of God is devoid of validity. For Aquinas, the existence of God needs to be demonstrated, and demonstration must start from the sensible world without any prejudice. (1) Such demonstrations are possible and are accommodated to anyone who is simply capable of reflecting. There are five ways in which the human intellect can prove the existence of God. All have a common point of resemblance. The starting point is a consideration of the sensible world known by immediate experience. Such a consideration of the sensible world would remain incomprehensible unless it was related to God as author of the world. So each argument might be reduced to a syllogism whose major premise is a fact of experience, and whose minor premise is a principle of reason, which brings to light the intelligibility of the major premise. It is interesting to note that Aquinas uses the Aristotelian principle of the priority of act over potency for the first three arguments. Where there is a being in change, i.e., passing from potency to actuality, there must be another being actually existent, outside the series in change, whether this series is considered to be finite or infinite. Aquinas formulates this principle in three different ways according to the three aspects of reality taken into consideration. For the first way the formulation is: What is moved, is moved by another; for the second way: It is impossible for something to be the efficient cause of itself; for the third way: What is not, cannot begin to be, unless by force of something which is. The fourth way takes into consideration many aspects of reality, which, when compared with one another, show that they are more or less perfect. The principle of intelligibility is the following: What is said to be the greatest in any order of perfection is also the cause of all that exists in that order. The fifth way takes into consideration the order of nature: Where there is a tendency of many to the same end, there must be an intellectual being causing such an order. Let us set forth the schematic structure of the five ways:
Thus, in brief, we have Aquinas' five proofs for the existence of God; proofs from the notion of motion, cause, contingency, perfection, and order. The proofs for the existence of God are also means of knowing something of God's essence. This knowledge, however, remains always essentially inadequate and incomplete. One way of knowing God is the way of negative theology, that is, by removing from the concept of God all that implies imperfection, potentiality, materiality. In other words, by this method we arrive at a knowledge of God through considering what He is not. A second method is that of analogy. God is the cause of the world. Now every object reflects some perfection of the cause from which it proceeds. Hence it is possible for the human mind to rise to the perfections of God from the consideration of the perfection it finds in creatures. This it does, naturally, by removing all imperfection and potentiality from the creatures considered. The resultant idea of the nature of God is thus had through analogy with the perfections of the created universe. References: (1) Summa Theol., Part I, q. 2, a.1; Contra Gent., I, 11.
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