Without the principle of final causes, could physiology proceed a single step, render to itself an account of a single organ, or determine a single function?
Is not the principle on which the whole of morals rests, the principle which obligates man to good and lays the foundation of virtue, of the same nature? Does it not extend to all moral beings, without distinction of time and place? Can you conceive of a moral being who does not recognize in the depth of his conscience that reason ought to govern passion, that it is necessary to preserve sworn faith, and, against the most pressing interest, to restore the treasure that has been confided to us?
And these are not mere metaphysical prejudices and formulas of the schools: I appeal to the most vulgar common sense.
If I should say to you that a murder has just been committed, could you not ask me when, where, by whom, wherefore? That is to say, your mind is directed by the universal and necessary principles of time, of space, of cause, and even of final cause.
If I should say to you that love or ambition caused the murder, would you not at the same instant conceive a lover, an ambitious person? This means, again, that there is for you no act without an agent, no quality and phenomenon without a substance, without a real subject.
If I should say to you that the accused pretends that he is not the same person who conceived, willed, and executed this murder, and that, at intervals, his personality has more than once been changed, would you not say he is a fool if he is sincere, and that, although the acts and the incidents have varied, the person and the being have remained the same?
Suppose that the accused should defend himself on this ground, that the murder must serve his interest; that, moreover, the person killed was so unhappy that life was a burden to him; that the state loses nothing, since in place of two worthless citizens it acquires one who becomes useful to it; that, in fine, mankind will not perish by the loss of an individual, &c.; to all these reasonings would you not oppose the very simple response, that this murder, useful perhaps to its author, is not the less unjust, and that, therefore, under no pretext was it permitted?
The same good sense which admits universal and necessary truths, easily distinguishes them from those that are not universal and necessary, and are only general, that is to say, are applied only to a greater or less number of cases.
For example, the following is a very general truth: the day succeeds the night; but is it a universal and necessary truth? Does it extend to all lands? Yes, to all known lands. But does it extend to all possible lands? No; for it is possible to conceive of lands plunged in eternal night, another system of the world being given. The laws of the material world are what they are; they are not necessary. Their Author might have chosen others. With another system of the world one conceives other physics, but we cannot conceive other mathematics and other morals. Thus it is possible to conceive that day and night may not be in the same relation to each as that in which we see them; therefore the truth that day succeeds night is a very general truth, perhaps even a universal truth, but by no means a necessary truth.
Montesquieu has said that liberty is not a fruit of warm climates. I acknowledge, if it is desired, that heat enervates the spirit, and that warm countries maintain free governments with difficulty; but it does not follow that there may be no possible exception to this principle: moreover, there have been exceptions; hence it is not an absolutely universal principle, much less is it a necessary principle. Could you say as much of the principle of cause? Could you in any way conceive, in any time and in any place, a phenomenon which begins to appear without a cause, physical or moral?