All the pieces of the machine of this world seem, however, made for each other. A few philosophers affect to mock at the final causes rejected by Epicurus and Lucretius. It is, it seems to me, at Epicurus and Lucretius rather that they should mock. They tell you that the eye is not made for seeing, but that man has availed himself of it for this purpose when he perceived that eyes could be so used. According to them, the mouth is not made for speaking, for eating, the stomach for digesting, the heart for receiving the blood from the veins and for dispatching it through the arteries, the feet for walking, the ears for hearing. These persons avow nevertheless that tailors make them coats to clothe them, and masons houses to lodge them, and they dare deny to nature, to the great Being, to the universal Intelligence, what they accord to the least of their workmen.
Of course one must not make an abuse of final causes; we have remarked that in vain Mr. Prieur, in "The Spectacle of Nature," maintains that the tides are given to the ocean so that vessels may enter port more easily, and to stop the water of the sea from putrefying. In vain would he say that legs are made to be booted, and the nose to wear spectacles.
In order that one may be certain of the true end for which a cause functions, it is essential that that effect shall exist at all times and in all places. There were not ships at all times and on all the seas; hence one cannot say that the ocean was made for the ships. One feels how ridiculous it would be to maintain that nature had worked from all time in order to adjust herself to the inventions of our arbitrary arts, which appeared so late; but it is quite evident that if noses were not made for spectacles, they were for smelling, and that there have been noses ever since there have been men. Similarly, hands not having been given on behalf of glove-makers, they are visibly destined for all the purposes which the metacarpal bones and the phalanges and the circular muscle of the wrist may procure for us.
Cicero, who doubted everything, did not, however, doubt final causes.
It seems especially difficult for the organs of generation not to be destined to perpetuate the species. This mechanism is very admirable, but the sensation which nature has joined to this mechanism is still more admirable. Epicurus had to avow that pleasure is divine; and that this pleasure is a final cause, by which are ceaselessly produced sentient beings who have not been able to give themselves sensation.
This Epicurus was a great man for his time; he saw what Descartes denied, what Gassendi affirmed, what Newton demonstrated, that there is no movement without space. He conceived the necessity of atoms to serve as constituent parts of invariable species. Those are exceedingly philosophical ideas. Nothing was especially more worthy of respect than the moral system of the true Epicureans; it consisted in the removal to a distance of public matters incompatible with wisdom, and in friendship, without which life is a burden. But as regards the rest of Epicurus' physics, they do not appear any more admissible than Descartes' channelled matter. It is, it seems to me, to stop one's eyes and understanding to maintain that there is no design in nature; and if there is design, there is an intelligent cause, there exists a God.
People present to us as objections the irregularities of the globe, the volcanoes, the plains of shifting sands, a few small mountains destroyed and others formed by earthquakes, etc. But from the fact that the naves of the wheels of your coach have caught fire, does it ensue that your coach was not made expressly to carry you from one place to another?
The chains of mountains which crown the two hemispheres, and more than six hundred rivers which flow right to the sea from the feet of these rocks; all the streams which come down from these same reservoirs, and which swell the rivers, after fertilizing the country; the thousands of fountains which start from the same source, and which water animal and vegetable kind; all these things seem no more the effect of a fortuitous cause and of a declension of atoms, than the retina which receives the rays of light, the crystalline lens which refracts them, the incus, the malleus, the stapes, the tympanic membrane of the ear, which receives the sounds, the paths of the blood in our veins, the systole and diastole of the heart, this pendulum of the machine which makes life.