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.
Within the Aristotelian system Nature is radically pervaded by Telos. It can become intelligible only if we see it as a universe through and through teleological.
In Chapters 4 to 6 of Physics II Aristotle discusses the problem of chance and spontaneity, complaining that: “There are some who ascribe this heavenly sphere and all the worlds to spontaneity. They say that the vortex arose spontaneously, i.e., the motion that separated and arranged in its present order all that exists.”16 The first thing Aristotle points out in this context is that chance cannot be the cause of what happens with constancy or for the most part.17 Constancy and determinateness cannot be caused by chance, for chance is the exact opposite to the latter. For Aristotle a thing comes to pass by nature or as a result of thought or by chance. The disjunction is absolute. Things which happen by nature or as a result of thought both belong to the class of things which are for the sake of something. 18 So chance is a name for incidental events which, however, are secondary by-products of actions by nature or deliberation. A per se cause by its nature is determinate, whereas incidental causes are indeterminable and indefinite.19 The incidental occurs and is possible only within the sphere of what happens by nature of deliberate intent. “It is clear then that chance is an incidental cause in the sphere of those actions for the sake of something, which involves purpose.”20
So chance is really not a cause stricto sensu. It is rather an unintended intersection of different events which happen by their nature or are deliberately intended. Therefore, it is “contrary to rule,”21 and as such it is unstable and “none of the things which result from it can be invariable or normal.” 22 Aristotle further explains that chance occurs only as the contrary of deliberate intention; hence it is possible only within the “moral sphere” or where deliberate intention is present, and thus he excludes it in inanimate things, lower animals, children. These cannot do anything by chance because of lack of deliberate intentionality in them. However, he grants to inanimate beings and animals spontaneity.23 Spontaneity results from an action “by nature” but one producing an unintended result under the influence of an external agent. Spontaneity connected with deliberate intention may result in “chance.” Both chance and spontaneity are sources of change since “in this sort of causation the number of causes is infinite.”24 Their effects remain always incidental and no incidental cause is prior to cause “per se.” “Hence, however true it may be that the heavens are due to spontaneity, it will be true that intelligence and nature will be prior causes of this All and of many things in it besides.”25
In the last statement we can clearly see that the universe is primarily caused by “intelligence and nature” and these two belong, as previously stated, to the class of agents which always act for an end, i.e., for “that for the sake of which.” Finality reigns there.
The evidence for the priority of finality is, for Aristotle, constancy and determinateness. Both are rooted in the metaphysical structure of each being and here the form is the final cause. Prime matter, being their potency, does not contain determination of any kind. We mean prime matter as such, because there certainly exists a “sequence of forms” in nature, and prime matter already informed, actualized by some form, seems to be “disposed” rather to this form than that one. There remains therefore the form in beings which contributes constancy, determinateness and finality to Nature. Those few remarks are only logical sequelae of what has been said before on the role of form within the Aristotelian notion of finality.
We already mentioned that for Aristotle chance is incidental, not truly even a cause per se, indeterminate and, so to say, a secondary by-product within the sphere of what happens “by nature and deliberation.” As such, chance can never be a source of finality in the universe in any sense whatsoever; it is by definition its very opposite and can be conceived only in reference to purpose and order. Direction towards ends is for Aristotle evident when works of nature are comparable to human actions whose purposiveness is obvious and cannot be denied. There exists a strong parallelism and similarity between human purposive activity and the activity of other beings in Nature. Aristotle says: “If, therefore, artificial products are for the sake of an end, so clearly also are natural products. The relation of the later to the earlier terms of the series is the same in both.”26
In another place he emphasizes again: “It is absurd to suppose that purpose is not present 27 because we do not observe the agent deliberating.” Deliberation is not necessarily present, for example, in art, though art is not thereby lacking purpose.
In any ordered series of steps in an action that tends to a completion, all earlier steps are for the sake of the last one. “Now surely as in intelligent action so in nature; so it is in each action if nothing interferes. Now intelligent action is for the sake of an end; therefore, the nature of things also is so. Thus if a house, e.g., had been a thing made by nature, it would have been made in the same way as it is now by art; and if things made by nature were made also by art they would come to be in the same way as by nature.”28
In human works we observe the determination of the earlier steps in action by the later and ultimately by the “completion” the end, the purpose in an intelligent activity. The former steps become “means” to the later steps which lead to completion in the series. “Future” dominates the “now.” The “now” is and is determined and produced for the sake of the “not yet” realized, but intended future achievement. The different elements of activity are united into a coordinated series and become members of a sequence of activities as means (moments in the whole flow of action) precisely because they are necessary and must exist in this and not in another sequence if the purpose is to be attained. So the very order and determinate sequence of realization, the ordering of many into a unified series of directed activities and the regularity with which this ordering necessarily occurs are leading to a purpose-completion. Directionality which is achieved through and by orderly sequence already defines the completion as future purpose. There is a similarity between human intelligent activity and activities that are accomplished by nature. If in human action the orderly relationship of the later to the earlier constitutes the finality of the whole activity it is clear that the same is done by works of nature.
This seems to be the core of the whole argument. Now since the activity of any being flows from its nature it reveals the purposive character of works of nature. Aristotle gives examples from the life and activities of birds and animals. Specifically he mentions spiders, ants; the way the swallow builds its nest, the spider the network, the ants their anthills. Later on he mentions plants, and seeds. Ultimately, since nature means primarily prime matter and form, the form remains the ultimate principle of action bearing the character of “that for the sake of which.” This action, however, is purposive, as has been shown.
Aristotle does not even suspect that the above line of argumentation would be attacked as anthropomorphism. He simply points to the same elements in human intelligent activity and the works of natural beings, living and non-living outside of the human sphere. Since he does not see any difference between the two, his reasoning is for him conclusive: “It is absurd to suppose that purpose is not present because we do not see the agent deliberating.” Thus he concludes firmly: “It is plain then that nature is a cause, a cause that operates for a purpose.”29