Leviathan rigorously argues that civil peace and social unity are best achieved by the establishment of a commonwealth through social contract. Hobbes's ideal commonwealth is ruled by a sovereign power responsible for protecting the security of the commonwealth and granted absolute authority to ensure the common defense. In his introduction, Hobbes describes this commonwealth as an "artificial person" and as a body politic that mimics the human body. The frontispiece to the first edition of Leviathan, which Hobbes helped design, portrays the commonwealth as a gigantic human form built out of the bodies of its citizens, the sovereign as its head. Hobbes calls this figure the "Leviathan," a word derived from the Hebrew for "sea monster" and the name of a monstrous sea creature appearing in the Bible; the image constitutes the definitive metaphor for Hobbes's perfect government. His text attempts to prove the necessity of the Leviathan for preserving peace and preventing civil war.
Leviathan is divided into four books: "Of Man," "Of Common-wealth," "Of a Christian Common-wealth," and "Of the Kingdome of Darknesse." Book I contains the philosophical framework for the entire text, while the remaining books simply extend and elaborate the arguments presented in the initial chapters. Consequently, Book I is given the most attention in the detailed summaries that follow. Hobbes begins his text by considering the elementary motions of matter, arguing that every aspect of human nature can be deduced from materialist principles. Hobbes depicts the natural condition of mankind--known as the state of nature--as inherently violent and awash with fear. The state of nature is the "war of every man against every man," in which people constantly seek to destroy one another. This state is so horrible that human beings naturally seek peace, and the best way to achieve peace is to construct the Leviathan through social contract.
Book II details the process of erecting the Leviathan, outlines the rights of sovereigns and subjects, and imagines the legislative and civil mechanics of the commonwealth. Book III concerns the compatibility of Christian doctrine with Hobbesian philosophy and the religious system of the Leviathan. Book IV engages in debunking false religious beliefs and arguing that the political implementation of the Leviathanic state is necessary to achieve a secure Christian commonwealth.
Hobbes's philosophical method in Leviathan is modeled after a geometric proof, founded upon first principles and established definitions, and in which each step of argument makes conclusions based upon the previous step. Hobbes decided to create a philosophical method similar to the geometric proof after meeting Galileo on his extended travels in Europe during the 1630s. Observing that the conclusions derived by geometry are indisputable because each of constituent steps is indisputable in itself, Hobbes attempted to work out a similarly irrefutable philosophy in his writing of Leviathan.