It then becomes possible to study methodically a given habit, or even the totality of the habits belonging to a given time and place, by following the table given above. The operation presents no difficulties of method in the case of those species of facts which appear as individual and voluntary habits--language, art, sciences, conceptions, private usages; here it is enough to ascertain in what each habit consisted. It is merely necessary to distinguish carefully between those who originated or maintained habits (artists, the learned, philosophers, introducers of fashions) and the mass who accepted them. But when we come to social or political habits (what we call institutions), we meet with new conditions which produce an inevitable illusion. The members of the same social or political group do not merely habitually perform _similar_ actions; they influence each other by _reciprocal_ actions, they command, coerce, pay each other. Habits here take the form of _relations_ between the different members; when they are of old standing, formulated in official rules, imposed by a visible authority, maintained by a special set of persons, they occupy so important a place in life, that, to the persons under their influence, they appear as external realities. The men, too, who specialise in an occupation or a function which becomes the dominating habit of their lives, appear as grouped in distinct categories (classes, corporations, churches, governments); and these categories are taken for real existences, or at least for organs of various functions in a real existence, namely, society. We follow the analogy of an animal's body so far as to describe the "structure" and the "functions" of a society, even its "anatomy" and "physiology." These are pure metaphors. By the structure of a society we mean the rules and the customs by which occupations and enjoyments are distributed among its members; by its functions we mean the habitual actions by which each man enters into relations with the others. It may be convenient to use these terms, but it should be remembered that the underlying reality is composed entirely of habits and customs.