Varying configurations of appetites and aversions constitute the various human “passions.” As Aristotle wrote, the metaphysical categories of good and evil are derived from our individual sensibilities of appetite and aversion: what we desire is “good” and what we avoid and direct our hate toward is “evil.” When a person decides whether to act, he or she “deliberates” on the good or evil merits of the various options. At the end of deliberation, the decision is called the will.
Hobbes’s materialist view of the world is built upon the belief that the universe is a plenum, meaning that it is composed entirely of bodies (and no empty space, or vacuum) and that everything that happens is a result of the motion of those bodies. He takes this view to surprising lengths, suggesting that human nature, encompassing our physical, mental, and emotional faculties, is a product of physical motions. Even the various human passions are explained by Hobbes in quantitative physical terms. The quantity and type of passion possessed by an individual defines his or her condition in the world: to have weak passion is “dullness,” to have indifferent passion is “giddiness,” to have an overabundance or disproportionate amount of passion is “madness.”
Another surprising and important assertion in the opening segment of Leviathan is that science and philosophy are equivalent endeavors. Hobbes is intent on illustrating the extent to which a proper philosophical method can explain and encompass all the varied areas of human knowledge. Unlike his contemporaries Francis Bacon and Robert Boyle, Hobbes does not believe in reaching true scientific knowledge through observation or experiment. Rather, he posits that all true science and philosophy must be based in language and in the solidity of definitions shared among many people, like the definitions of geometry. To Hobbes, “science is the knowledge of the consequence of words.” He demands logically built definitions that take universally accepted first principles as their base, rather than subjective opinions or articles of faith. Following the form of geometry, Hobbes demonstrates how his own philosophical model can take under its umbrella the whole of human scientific inquiry.