This positive transformation of the doctrine of final causes had already been clearly sketched by the philosophers of the XVIII. century whom Comte knew very well, by Diderot, by Hume, by d’Holbach. Hume says, for instance,[66] “It is useless to insist upon the uses of parts in animals or in plants, and on their curious adaptation one to another. I should much like to know how an animal could subsist without this adaptation. Do we not see that if it ceases he perishes at once, and that the matter of which he was composed takes some other shape?” And d’Holbach, “These wholes would not exist in the form which they bear, if their parts ceased to act as they do; that is to say, ceased to be arranged in such a way as to lend themselves to being mutually helpful to each other. To be surprised that the heart, the brain, the eyes, the arteries, etc., of an animal act as they do; or that a tree produces fruit, is to be surprised that a tree or an animal exists. These beings would not exist or would no longer be what they are, if they ceased to act as they do: this is what happens when they die.”[67]
Comte makes this criticism of the doctrine of final causes his own. But, faithful to his maxim, “We only destroy what we replace,” he claims to substitute a positive principle to this metaphysical doctrine, which preserves the elements in it which are compatible with the scientific method. It is the principle of the conditions of existence. In virtue of this principle, by the very fact that such an organ is part of such a living being, it necessarily co-operates in a determined although perhaps unknown manner, with the totality of the acts which make up its existence: an organ no more exists without a function than a function without an organ. But it in no way follows from this that all the organic functions are performed as perfectly as we could imagine them to be. For instance pathological analysis demonstrates that the disturbing action of each organ upon the whole of the economy is very far from being always compensated for by its utility in the normal state. “If, within certain limits, everything is necessarily arranged in such a way as to be able to exist, we should seek in vain, in the majority of effective arrangements, for proofs of a wisdom superior or even equal to human wisdom.”[68]
Extending these considerations to the whole of the phenomena known to us, Comte concludes in almost the same way as Cournot will later on. An order establishes itself in nature, since it subsists, since it is intelligible, since there are laws.[69] Does not the very idea of a law induce at once the corresponding idea of a certain spontaneous order? But “this consequence is not more absolute than the principle from which it is derived.”[70] The experience which reveals this order to us also shows us that it is imperfect, of an imperfection which grows with the complexity of phenomena. Every time that the necessary and sufficient conditions are realised for a natural system to be able to exist, this system exists in fact, however full of imperfections it may be in other respects. “Undoubtedly, an inevitable necessity which links together a series of events, and a premeditated plan which directs them, resemble each other very much so far as the consequences are concerned.”[71] But, if the necessity is established, there is no need to suppose the plan. Now the principle of the conditions of existence, in showing that all that is “indispensable,” is at the same time “inevitable,” renders this supposition superfluous.
A double tendency makes itself felt in this theory. On the one hand Comte, faithful to the spirit of his philosophy, rejects all that claims to go beyond experience, that is to say the transcendental hypothesis of final causes and of optimism. On the other hand, he wishes to account for the order of nature, which is a fact. Now this order, all imperfect as it is, implies not only the existence of laws, but moreover a permanent harmony between these laws. “The present is full of the past, and big with the future.” The principle of the conditions of existence explains this permanence of order, at least as much as it needs to be explained from the positive point of view. For it states that everywhere, in fact, the dynamical laws are in harmony with the statical laws, and that “progress is a development of order.” The principle of the conditions of existence is no more a priori than the principle of laws. Like it it is founded upon an “immense induction.” Like it again, it only acquires its full power when social science is created, and positive philosophy established.
Should we not be tempted to see in this doctrine a kind of projection of an idealism such as that of Leibnitz on the lines of positive thought? Just as Leibnitz makes mechanism rest upon a deeper dynamism, so Comte completes the principle of laws by the principle of the conditions of existence. True, between these two doctrines there lies all the distance which separates the positive from the metaphysical spirit. But none the less both give symmetrical solutions of the same problem which correspond to one another, the one a priori the other a posteriori.
IV.
All natural laws, must be conceived as rigorously invariable, whether it be a question of mathematical or of sociological laws. If we could conceive, in any case, that under the influence of conditions exactly similar the phenomena should not remain perfectly identical, not only in kind, but also in degree, all scientific theory would at once become impossible.[72] This principle is the very condition of the possibility of prevision, and consequently of positive science. Claude Bernard will call it “the absolute determinism of phenomena.” Comte admits no absolute: but he considers nevertheless that the invariability of natural laws does not permit of exception.
In the case of certain laws their invariability can be directly verified, since they come before us in a mathematical form. Such are, for instance, the mechanical, astronomical and physical laws. Others, on the contrary, such as the biological laws, refuse to be dealt with by numbers and cannot be reduced to equations. But this evidently comes from their complexity: “If it were possible rigorously to isolate each one of the simple causes which concur in producing the same physiological phenomenon, everything tends to show that under well determined circumstances, it would appear to be possessed of a kind of influence and of a quantity of action, as exactly fixed as we see it to be in universal gravitation.”[73] Every elementary phenomenon has its curve.
If then in all cases we could go back to the elementary phenomena, we could undoubtedly also formulate their mathematical law. In this sense, mathematical analysis would apply to all the phenomena of the world without exception. But, nearly always, the decomposition of given phenomena into elementary phenomena is impossible to us. At any rate the work of synthesis or of re-composition taken in the reverse order is far beyond our mathematical powers. The only phenomena to which we apply the analysis without too much trouble are the most simple of all, the geometrical and mechanical phenomena. The difficulty grows very rapidly with the complication of astronomical, physical, and especially chemical phenomena. When we reach the realm of living nature, the elementary phenomena escape us altogether. They are given to us in a state of almost infinite complexity, and, in virtue of the biological consensus, closely bound up with others of no less complex a character. These phenomena are in themselves syntheses depending upon other syntheses all in a state of mutual influence and of constant instability. Then, although, in principle, it remains true that identical antecedents can only have identical consequents, in fact, because of the very great number of elementary actions which concur in the production of each phenomenon, there have perhaps never been, there perhaps never will be, two cases rigorously similar.
It follows that we must not confuse “the subordination of any events whatever to invariable laws with their irresistible necessary accomplishment.”[74] Relatively single phenomena appear indeed to us to be produced with an irresistible necessity: for instance, the facts of gravitation. But complex phenomena, in virtue of the more and more varied combinations which their several necessary conditions admit of no longer present this character. They are more “modifiable” and less “irresistible.” In other words, as one considers more elevated, more complex, more “noble” categories of facts, the laws become removed from the type of mathematical necessity, and admit more of an ever increasing element of “contingency”?