74. Philosophers have been much troubled about the origin of forms, of Entelechies, or souls. But at the present day, when, by accurate investigations of plants, insects and animals, they have become aware that the organic bodies of nature are never produced from chaos or from putrefaction, but always from seed, in which undoubtedly there had been a preformation; it has been inferred that not only the organic body existed in that seed before conception, but also a soul in that body—in one word, the animal itself—and that, by the act of conception, this animal is merely disposed to a grand transformation, to become an animal of another species. We even see something approaching this, outside of generation, as when worms become flies, or when caterpillars become butterflies.
75. Those animals, of which some are advanced to a higher grade, by means of conception, may be called spermatic; but those among them which remain in their kind—that is to say, the greater portion—are born, multiply, and are destroyed, like the larger animals, and only a small number of the elect among them, pass to a grander theatre.
76. But this is only half the truth. I have concluded that if the animal does not begin to be in the order of nature, it also does not cease to be in the order of nature, and that not only there is no generation, but no entire destruction—no death, strictly considered. And these a posteriori conclusions, drawn from experience, accord perfectly with my principles deduced a priori, as stated above.
77. Thus we may say, not only that the soul (mirror of an indestructible universe) is indestructible, but also the animal itself, although its machine may often perish in part, and put off or put on organic spoils.
78. These principles have furnished me with a natural explanation of the union, or rather the conformity between the soul and the organized body. The soul follows its proper laws, and the body likewise follows those which are proper to it, and they meet in virtue of the preëstablished harmony which exists between all substances, as representations of one and the same universe.
79. Souls act according to the laws of final causes, by appetitions, means and ends; bodies act according to the laws of efficient causes, or the laws of motion. And the two kingdoms, that of efficient causes and that of final causes, harmonize with each other.
80. Des Cartes perceived that souls communicate no force to bodies, because the quantity of force in matter is always the same. Nevertheless, he believed that souls might change the direction of bodies. But this was because the world was at that time ignorant of the law of nature, which requires the conservation of the same total direction in matter. Had he known this, he would have hit upon my system of preëstablished harmony.
81. According to this system, bodies act as if there were no souls, and souls act as if there were no bodies; and yet both act as though the one influenced the other.
82. As to spirits, or rational souls, although I find that at bottom the same principle which I have stated—namely, that animals and souls begin with the world and end only with the world—holds with regard to all animals and living things, yet there is this peculiarity in rational animals, that although their spermatic animalcules, as such, have only ordinary or sensitive souls, yet as soon as those of them which are elected, so to speak, arrive by the act of conception at human nature, their sensitive souls are elevated to the rank of reason and to the prerogative of spirits.
83. Among other differences which distinguish spirits from ordinary souls, some of which have already been indicated, there is also this: that souls in general are living mirrors, or images of the universe of creatures, but spirits are, furthermore, images of Divinity itself, or of the Author of Nature, capable of cognizing the system of the universe, and of imitating something of it by architectonic experiments, each spirit being, as it were, a little divinity in its own department.