Hobbes believed that all phenomena in the universe, without exception, can be explained in terms of the motions and interactions of material bodies. He did not believe in the soul, or in the mind as separate from the body, or in any of the other incorporeal and metaphysical entities in which other writers have believed. Instead, he saw human beings as essentially machines, with even their thoughts and emotions operating according to physical laws and chains of cause and effect, action and reaction. As machines, human beings pursue their own self-interest relentlessly, mechanically avoiding pain and pursuing pleasure. Hobbes saw the commonwealth, or society, as a similar machine, larger than the human body and artificial but nevertheless operating according to the laws governing motion and collision.
In putting together this materialist view of the world, Hobbes was influenced by his contemporaries Galileo and Kepler, who had discovered laws governing planetary motion, thereby discrediting much of the Aristotelian worldview. Hobbes hoped to establish similar laws of motion to explain the behavior of human beings, but he was more impressed by Galileo and Kepler’s mathematical precision than by their use of empirical data and observation. Hobbes hoped to arrive at his laws of motion deductively, in the manner of geometrical proofs.
It is important to note that Hobbes was not in any position to prove that all human experience can be explained in terms of physical and mechanical processes. That task would have required scientific knowledge far beyond that possessed by the 17th century. Even today, science is cannot fully explain human experience in physical terms, even though it is believed that science will eventually be able to do just that. In the absence of such a detailed explanation, the famous image of the human being as a machine in Hobbes’s writing remains more of a metaphor than a philosophical proof.