Aristotle is the first philosopher in the Greek tradition who developed the full technical analysis of final cause. He is fully aware of that fact and expresses this awareness when he criticizes his predecessors for failing to understand the crucial value of final cause.for any serious philosophical explanation of reality.1 This philosophy of final cause is found mainly in the first book of his Metaphysics and the second book of Physics. Occasionally he develops the concept of final cause in other places within the body of his writings. The Aristotelian notion of final cause deserves a thorough examination on two counts: (a) he is the first one to give complete metaphysical analysis of final cause, and (b) he influenced in this respect very deeply the thought of Thomas Aquinas and many other thinkers in the West.
Without a clear knowledge of change (or motion) there is no understanding of the nature of things since by nature Aristotle understands that which is the origin of motion and change. “For those things are natural which by a continuous movement originated from an internal principle arrive at some completion, but always the tendency is towards the same end if there is no impediment.” 2 The essential meaning of “nature” is for Aristotle “…the essence of those things, which have the principle of movement in themselves, insofar as they are this something.”3
Nature therefore contains the following elements: (a) it is a principle, a metaphysical beginning or a source, (b) a principle of movement or change, (c) it is internal, constitutive of the essence of a being, (d) it is a tendency to a determined end, (e) it is a tendency towards a state of completion, perfection, actualization.
From the above it is clear that the analysis of change is the central focus of the Aristotelian Metaphysics and his Philosophy of Nature. Confronted with the Parmenidean monism of immutable being, on the one hand, and the obvious, omnipresent and real fact of change on the other, Aristotle gave a masterly metaphysical analysis of change and becoming in dynamical terms. Basic Aristotelian insight in this respect remains true even today. We shall also see that every natural change is intelligible to him only through the notion of final cause.
In order to solve the problem of change in general, Aristotle introduces the notion of potency. This notion of “potency” as correlative to “act” makes change intelligible. The thing which is changing is in the process of transition from one mode (terminus a quo), to another mode of being (terminus ad quern). There are two main types of such transition: one, called accidental, when one and the same being changes and acquires a new state retaining its proper nature; a second, called substantial, when the transition is from one nature to another, a different one. One being ceases to exist and a new one emerges. At this point we are interested in the first type of change. It occurs in beings composed of potency and act.
Potency as a metaphysical and internal component is openness, possibility, capacity for a being to move from one actual mode of existing to another, a new one. It makes newness intelligible. By newness here we understand the gradual transition to the “terminus ad quem.” This transition is always a “transition toward,” never something in itself, but it is a movement of something which itself changes. Something can be in the movement of change only insofar as it is actually not yet completed, not having yet what it can have, not completely realized. It cannot at “terminus a quo” be already what it becomes at “terminus adquem”. The changing movement is therefore defined by Aristotle as realization of the potential as such.4
A being can exist in three possible modes: (a) it is not yet moving, (b) it is in the mode of complete realization, full completion; then it moves no more, (c) it is in the middle mode of movement-change, in the transition from one mode of being to another, to its realization.
Change, therefore, is a state of a being which does not yet fully realize all the potency of “this something” It still is in the position to acquire new “points of completion.” Each natural change is an internal going towards its end perfection, or full realization: towards its final completion. Each natural movement is for the “where-for” or the “good” for which the movement occurs. Each natural movement has an aim. This, however, is the Aristotelian definition of final cause 5 proposed, e.g., in Metaphysics (Bk. XII, Chap. 1): “For final cause is (a) some being for whose good an action is done, and (b) something at which the action aims.”6 Since we are considering here internal directionality towards final actualization, this actualization is precisely “that for the sake of which” and „that at which the action aims.” Both are Aristotelian definitions of final cause.
It remains to show that the internal finality in natural beings is identical with the form as final cause. Form is the essence of “that which is coming to be.”7 For it is clear that the Aristotelian notion of finality is rooted in the analysis of motion-change. This analysis, as mentioned above, makes the notion of “nature” very clear. As a matter of fact, for Aristotle both nature and internal final cause are identical.
According to Aristotle nature is (a) a principle of movement and rest within a thing (all beings that have such a principle are “natural,” they act by “nature”), (b) nature constitutes the essence of a “this something,” (c) nature is the source of the tendency and action-movement towards actualization.
We already noticed that form contributes to a being its actuality, its essence, and it constitutes the being's internal finality. It is the final cause inside the thing. Aristotle identifies “nature” many times in his writings with “essence,” “whatness,” and consequently with form. “The term according to nature” is applied to all these things and also to the attributes which belong to them in virtue of what they are.” 8 In another place he says „The form is ‘nature' rather than matter.”9
The nature of a thing is revealed in the process of growth (change) by which its complete fullness is attained. The internal movement is initiated by nature, but on the other hand, nature is attained, completely realized in that process. Then Aristotle expressly affirms: “But the nature is the end or “that for the sake of which.”10 But “that for the sake of which” means what is best and the end of things that lead up to it.11
To confirm this further Aristotle stresses: “Now, the causes being four, it is the business of the physicist to know about them all, and if he refers his problems back to all of them, he will assign the 'why' proper to his science–the matter, the form, the mover, that for the sake of which. The last three often coincide for the 'what' and ‘that for the sake of which’ are one.”12
Nature itself therefore plays the role of final cause. This identity is very clearly stated by Aristotle: “Therefore action for an end is present in things which come to be and are by nature.”13 Both artificial and natural products are therefore for ends. Aristotle mentions animals other than man which make things neither by art nor after deliberation: spiders, ants. He also mentions plants.
If then it is both by nature and for an end that the swallow makes its nest and the spider its web, and plants grow leaves for the sake of the fruit and send their roots down (not up) for the sake of nourishment, it is plain that this kind of cause is operative in things which come to be and are by nature. And since “nature” means two things, the matter and the form, of which the latter is the end, and since all the rest is for the sake of the end, the form must be the same in the sense of “that for the sake of which.”14
Aristotle concludes: “It is absurd to suppose that purpose is not present because we do not observe the agent deliberating.”15 It is clear from the above quotations that for Aristotle all natural tendency is finally directed. Nature is operating for a purpose. Change as natural tendency is self-realization at which the transition aims. This “aim” or “end” is the actualizing or the full completion of the form, which, as Aristotle stated above, very often is identified with “that for the sake of which,” the purpose, the goal: the final cause.
Finality therefore or purposiveness is rooted in the very nature of all natural beings. It can be stated that this is a fundamental principle of the entire universe. Aristotle affirms towards the end of the Physics that anyone who denies finality in Nature denies natures themselves.