Teleology is seldom used according to its etymological meaning to denote the branch of philosophy which deals with ends or final causes. It means the doctrine that there is design, purpose, or finality in the world, that effects are in some manner intentional, and that no complete account of the universe is possible without reference to final causes (for the notion of final cause, see CAUSE). With mechanism teleology admits the determinism of physical efficient causes. It also acknowledges that the object of scientific research is to discover the laws of phenomena, and that any fact is scientifically explained when adequate causes are assigned to it, and the conditions of its occurrence are known. But against mechanism, teleology claims that this determinism, these laws, and the mode of activity of efficient causes reveal the existence of a directive principle and of finality in the works of nature. Hence the question is not whether there are efficient or final causes, whether, for instance, man sees because he has eyes or has eyes in order to see. Final causes and efficient causes are not mutually exclusive. It must be admitted that any result in nature is to be ascribed to an unbroken chain of active causes, and the function of the final cause is not to supply any missing link but to explain how the activity of efficient causes is directed toward useful results. Nor can the teleologist be asked to indicate the end of every activity any more than the mechanist can be required to indicate the efficient cause of every phenomenon. Finally the problem does not refer to conscious and intelligent finality such as is manifested in human purposive actions, for it is obvious that in many of his actions man is guided by the idea of a preconceived plan which he endeavours to realize. Human works are for something; the house is built to live in; the clock is made to keep time; the machine is constructed to perform some work; the statue is carved to realize some ideal; etc. Are we justified in speaking of the works of nature in the same way? When we speak of ends and purposes in nature do we not attribute to it that which is distinctly human? Do we not carry too far the process of personification and analogy, and thereby incur the reproach of anthropomorphism? According to mechanists, because we foresee results we falsely conclude that nature strives to realize them. Ends exist in the mind which studies nature, not in nature itself. To admit ends is mentally to reverse the natural process, to look upon the effect as a cause, and from it to ascend the causal series regressively.

I. It is important at first to make a distinction between extrinsic and intrinsic finality. The former consists in realizing an end which is outside of the being that realizes it, and thus in contributing to the utility and welfare of other beings. In this way the mineral is utilized by the plant, and the plant by the animal. Or again the heat of the sun is a condition of growth and development. From this extrinsic finality result the subordination of various beings, and the order and harmony of the universe. But while extrinsic finality seems obvious in several instances many of its details escape us, and it is easy to make a wrong use of it by attributing false or childish ends to every being and event, and by taking a narrow anthropocentric view of finality. This abuse of final causes called for the vigorous protests of Bacon ("De Dignitate et Augmentis Scientiarum," III, iv), Descartes ("Principia Philosophiæ", I, 28; III, 2, 3; "Meditationes", III, IV), Spinoza (Ethica, I, prop. 36 app.). The exclusive consideration of extrinsic ends contributed probably more than any other cause to the discredit into which teleology fell at the time of the Renaissance. Yet, as Voltaire rightly remarks, it is clear that if the nose was not made to wear spectacles, it was made for the sense of smell (Dictionnaire philosophique, s. v. Causes finales). Here Voltaire appeals to the principle of intrinsic finality which, according to Aristotle and St. Thomas, is primary, while extrinsic finality is derived and secondary.

Intrinsic finality consists in the fact that every being has within itself a natural tendency whereby its activity is directed towards the perfection of its own nature. "As the influx of the efficient cause consists in its own action, so the influx of the final cause consists in its being sought after and desired" (St. Thomas, "De veritate", Q. xxii, a. 2). But this desire or is not necessarily conscious. St. Thomas does not hesitate to speak of "natural appetite", "natural inclination", and even "intention of nature", to mean that every being has within itself a directive principle of activity. The final cause is a good which satisfies a tendency springing immediately from the nature of every being. "By the form which gives it its specific perfection, everything in nature has an inclination to its own operations and to its own end, which it reaches through these operations. Just as everything is, such also are its operations and its tendency to what is suitable to itself" (St. Thomas, "Contra Gentiles", IV, xix). Accordingly, God does not direct creatures to their ends from outside, but through their own nature. This teleological view does not suppose that every efficient cause in the world is directed immediately by an intelligence, but by its own natural tendency. The Divine plan of creation is carried out by the various beings themselves acting in conformity with their nature. When, however, this finality is called immanent, this expression must not be understood in a pantheistic sense, as if the intelligence which the world manifests were to be identified with the world itself, but in the sense that the immediate principle of finality is immanent in every being.

II. Thus understood the principle of teleology seems almost obvious. Activity is essential to every being, and the same substance, placed in the same conditions, always acts in the same way. Its effect, therefore, does not happen by chance, for chance cannot account for fixity and stability. Within the substance itself must be found a principle of determination. Now what is a determination but an adaptation and an orientation toward an end? The fact that the world is governed by laws, far from giving any support to the mechanistic conception, is rather opposed to it. A law is not a cause, but the expression of the constant manner in which causes produce their effects. To say that there are laws is simply to state the determinism of nature, and it is precisely to this determinism that St. Thomas appeals to establish teleology. "Every active cause acts for an end, otherwise from its activity one effect would not result rather than another, except by chance" (Summa Theologica I:44:4). And again: "It is necessary that every active cause should act for an end. For in a series of causes, if the first be removed, the others also are removed (i.e., fail to produce their effects). But the final cause is the first of all causes. The reason is that matter does not receive a form (i.e., does not change) except through the influence of an active cause. For nothing of itself passes from potentia to actus (see ACTUS ET POTENTIA), and the active cause does not act except in consequence of the intention of an end. Otherwise, if the active cause were not determined to produce some particular effect, it would not produce this rather than some other. In order to produce a determined effect, it must, therefore, be determined to something in particular which serves as an end. As in rational beings this determination takes place through the rational appetite or will, so in other beings it takes place through a natural inclination which is called natural appetite" (Summa Theologica I-II:1:2).

Efficient causes are not indifferent, and their effects are not fortuitous. As a matter of fact, from the many individual activities of the various beings of the world order and harmony result in the universe. And when different forces converge toward a harmonious result, their convergence cannot be explained except by admitting that they tend to realize a plan. Life is essentially teleological. There is a co-ordination of all the organs, the functions of every one depending on those of the others, and tending to the welfare of the whole organism. Little by little the primitive cell develops according to the general type of the species and evolves into the complete organism. To Aristotle's statement that "nature adapts the organ to the function, and not the function to the organ" (De partib., animal., IV, xii, 694b; 13), Lucretius replied: "Nothing in the body is made in order that we may use it. What happens to exist is the cause of its use" (De nat. rerum, IV, 833; cf. 822-56), — an objection which had been presented more forcibly by Aristotle himself (Phys., II, viii, 198b). The function, it is true, is the result of the organ; the eye sees because it is an eye, and, in general, every function is an effect of active causes. But what is not explained by mechanism is the convergence of many different causes toward a given result. If organs are so many mechanisms, it remains to be indicated how these mechanisms were organized. If appeal is made to evolution, it must be remembered that evolution is not a cause, but a mode of development, and that organic evolution rather accentuates the need of final causes. In the inorganic world, the constancy of the laws of nature and the resulting order of the world manifest the existence in every being of a principle of direction and orientation.

The fundamental defect of mechanism consists in giving exclusive attention to the analyzing of every event into its causes, and in forgetting to look for the reason of their synthesis. If we take a clock to pieces, we discover in it nothing but springs, wheels, pivots, levers etc. When we have explained the mechanism which ultimately causes the revolutions of the hands on the dial, shall we say that the clock was not made to keep time? The intelligence that designed it is not in the clock itself which now obeys its own laws. Yet in reality we have an adaptation of means to an end. Thus the unconscious finality in the world leads to the conclusion that there must be an intelligent cause of the world. The whole preceding doctrine is well summed up in the following passage from St. Thomas (Summa Theologica I:103:1 ad 3um): "The natural necessity inherent in things that are determined to one effect is impressed on them by the Divine power which directs them to their end, just as the necessity which directs the arrow to the target is impressed on it by the archer, and does not come from the arrow itself. There is this difference, however, that what creatures receive from God is their nature, whereas the direction imparted by man to natural things beyond what is natural to them is a kind of violence. Hence, as the forced necessity of the arrow shows the direction intended by the archer, so the natural determinism of creatures is a sign of the government of Divine Providence".

FARGES, Théorie fondamentale de l'acte de la puissance (7th ed., Paris, 1909); FLINT, Theism (London, 1889); GUTBERLET, Allgemeine Metaphysik (Münster, 1906); IDEM, Der mechanische Monismus (Paderborn, 1893); JANET, Les causes finales (Paris, 1882), tr. by AFFLECK (Edinburgh, 1883); MERCIER, Métaphysique générale (Louvain, 1905); PESCH, Institutiones philosophiœ naturalis (Freiburg, 1880); SULLY-PRUDHOMME AND RICHET, Le problème des causes finales (Paris. 1902); DE VORGES, Cause efficiente et cause finale (Paris, 1889); BALDWIN AND MOORE in Dict. of Philos. and Psychol. (New York, 1901), s. v.; EISLER, Wörterbuch der philosophischen Begriffe (Berlin, 1910), s. v. Zweck, etc.

C.A. DUBRAY