The influence of Descartes upon La Mettrie cannot be questioned but it is more difficult to estimate the influence upon him of materialistic philosophers. Hobbes published “The Leviathan” in 1651 and “De Corpore” in 1655. Thus he wrote about a century before La Mettrie, and since the eighteenth century was one in which the influence of England upon France was very great, it is easy to suppose that La Mettrie had read Hobbes. If so, he must have gained many ideas from him. The extent of this influence is, however, unknown, for La Mettrie rarely if ever quotes from Hobbes, or attributes any of his doctrines to Hobbes.
In the first place, both Hobbes and La Mettrie are thoroughgoing materialists. They both believe that body is the only reality, and that anything spiritual is unimaginable.[8] Furthermore their conceptions of matter are very similar. According to La Mettrie, matter contains the faculty of sensation and the power of motion as well as the quality of extension.[9] This same conception of matter is held by Hobbes, for he specifically attributes extension and motion to matter, and then reduces sensation to a kind of internal motion.[10] Thus sensation also may be an attribute of matter. Moreover Hobbes and La Mettrie are in agreement on many smaller points, and La Mettrie elaborates much that is suggested in Hobbes. They both believe that the passions are dependent on bodily conditions.[11] They agree in the belief that all the differences in men are due to differences in the constitution and organization of their bodies.[12] They both discuss the nature and importance of language.[13]
Hobbes differs from La Mettrie in holding that we can be sure that God exists as the cause of this world.[14] However even though he thinks that it is possible to know that God exists, he does not believe that we can know his nature.
La Mettrie’s system may be regarded as the application of a system like that of Hobbes to the special problem of the relation of soul and body in man; for if there is nothing in the universe but matter and motion, it inevitably follows that man is merely a very complicated machine.
There is great similarity also between the doctrine of La Mettrie and that of Toland. It is interesting to note the points of resemblance and of difference. Toland’s “Letters to Serena,” which contain much of his philosophical teaching, were published in 1704. There is a possibility therefore that La Mettrie read them and gained some suggestions from them.
The point most emphasized in Toland’s teaching[15] is that motion is an attribute of matter. He argues for this belief on the ground that matter must be essentially active in order to undergo change,[16] and that the conception of the inertness of matter is based on the conception of absolute rest, and that this absolute rest is nowhere to be found.[17] Since motion is essential to matter, there is no need, Toland believes, to account for the beginning of motion. Those who have regarded matter as inert have had to find some efficient cause for motion, and to do this, they have held that all nature is animated. But this pretended animation is utterly useless, since matter is itself endowed with motion.[18] The likeness to La Mettrie is evident. La Mettrie likewise opposes the doctrine of the animation of matter, and the belief in any external cause of motion.[19] Yet he feels the need of postulating some beginning of motion,[20] and although he uses the conception so freely, he does not agree with Toland that the nature of motion is known. He believes that it is impossible to know the nature of motion,[21] while Toland believes that the nature of motion is self-evident.[22]
Another point of contrast between Toland and La Mettrie is in their doctrines of God. Toland believes that God, “a pure spirit or immaterial being,” is necessary for his system,[23] while La Mettrie questions God’s existence and insists that immateriality and spirituality are fine words that no one understands.
It must be admitted, in truth, that La Mettrie and Toland have different interests and different points of view. Toland is concerned to discover the essential nature of matter, while La Mettrie’s problem is to find the specific relation of body and mind. On this relation, he builds his whole system.
b. The Relation of La Mettrie to an English Sensationalist: John Locke (1632–1704).
Locke’s “Essay Concerning Human Understanding” was published in 1690, and La Mettrie, like most cultured Frenchmen of the Enlightenment, was influenced by his teaching. The main agreement between Locke and La Mettrie is in their doctrine that all ideas are derived from sensation. Both vigorously oppose the belief in innate ideas,[24] teaching that even our most complex and our most abstract ideas are gained through sensation. But La Mettrie does not follow Locke in analyzing these ideas and in concluding that many sensible qualities of objects—such as colors, sounds, etc.—have no existence outside the mind.[25] He rejects Locke’s doctrine of spiritual substances,[26] and opposes Locke’s theistic teaching, laying stress, on the other hand, upon Locke’s admission of the possibility that “thinking being may also be material.”[27]