The central idea of Plato's model Republic, is the correspondence between the parts of a society and the faculties of the human mind. Classifying these faculties under the heads of Reason, Will, and Passion, he classifies the members of his ideal society under what he regards as three analogous heads:--councillors, who are to exercise government; military or executive, who are to fulfil their behests; and the commonalty, bent on gain and selfish gratification. In other words, the ruler, the warrior, and the craftsman, are, according to him, the analogues of our reflective, volitional, and emotional powers. Now even were there truth in the implied assumption of a parallelism between the structure of a society and that of a man, this classification would be indefensible. It might more truly be contended that, as the military power obeys the commands of the Government, it is the Government which answers to the Will; while the military power is simply an agency set in motion by it. Or, again, it might be contended that whereas the Will is a product of predominant desires, to which the Reason serves merely as an eye, it is the craftsmen, who, according to the alleged analogy, ought to be the moving power of the warriors. Hobbes sought to establish a still more definite parallelism: not, however, between a society and the human mind, but between a society and the human body. In the introduction to the work in which he develops this conception, he says-- "For by art is created that great LEVIATHAN called a COMMONWEALTH, or STATE, in Latin CIVITAS, which is but an artificial man; though of greater stature and strength than the natural, for whose protection and defence it was intended, and in which the _sovereignty_ is an artificial _soul_, as giving life and motion to the whole body; the _magistrates_ and other _officers_ of judicature and execution, artificial _joints_; _reward_ and _punishment_, by which, fastened to the seat of the sovereignty, every joint and member is moved to perform his duty, are the _nerves_, that do the same in the body natural; the _wealth_ and _riches_ of all the particular members are the _strength_; _salus populi_, the _people's safety_, its _business_; _counsellors_, by whom all things needful for it to know are suggested unto it, are the _memory_; _equity_ and _laws_ an artificial _reason_ and _will_; _concord_, _health_; _sedition_, _sickness_; and _civil war_, _death_."