The mind is so intimately dependent upon the condition and relation of the organs of the body, that if any means can ever be found to render men wiser and more ingenious than hitherto, I believe that it is in medicine they must be sought for.The work of Locke, Condillac, and Hartley argued that the mind is a tabula rasa, a blank slate, on which the environment leaves impressions through the senses. Perception and even cognition are treated not as acts requiring volition, but as the inevitable consequence of the impression of stimuli on the senses. La Mettrie gives the most forcible expression of this theory in L'homme machine (1748):
As a violin string or a harpsichord key vibrates and gives forth sound, so the cerebral fibers, struck by waves of sound, are stimulated to render or repeat the words that strike them. And as the structure of the brain is such that when eyes well formed for seeing, have once perceived the image of objects, the brain can not help seeing their images and their differences, so when the signs of these differences have been traced or imprinted in the brain, the soul necessarily examines their relations.Others took these modest generalizations further, arguing against the notion of a transcendent human nature, and advocating instead a model whereby the characters of humans are dependent entirely on the stimulti to which they are exposed. Montesquieu argued for the importance of environmental determination; he pointed to the strong but barbaric inhabitants of northern climates, compared to the refined and intellectual but delicate southerners. Scientists such as Boerhaave and (most famously) La Mettrie provided a scientific basis to the theory. La Mettrie's conclusion to L'homme machine notable for its directness:
Let us then conclude boldly that man is a machine, and that in the whole universe there is but a single substance differently modified.Although Linnaeus resisted strict mechanical explanations of behavior early in his career, he gave increasing credence to the belief, as reflected in his revisions to the twelve editions of the Systema naturae that appeared in his lifetime. Lamarck, however, while granting that the behavior of the most primitive species is determined by their environment, believed that more advanced species grew increasingly self-determined.
Mechanism had implications beyond the sciences, and could be extended from simple biology to other human endeavors. La Mettrie, for instance, applies the model to education in L'homme machine:
Nothing, as any one can see, is so simple as the mechanism of our education. Everything may be reduced to sounds or words that pass from the mouth of one through the ears of another into his brain. At the same moment, he perceives through his eyes the shape of the bodies of which these words are the arbitrary signs.