The study of institutions, however, obliges us to ask special questions about persons and their functions. In respect of social and economic institutions we have to ask what was the principle of the division of labour and of the division into classes, what were the professions and classes, how were they recruited, what were the relations between the members of the different professions and classes. In respect of political institutions, which are sanctioned by obligatory rules and a visible authority, two new series of questions arise. (1) Who were the persons invested with authority? When authority is divided we have to study the division of functions, to analyse the _personnel_ of government into its different groups (supreme and subordinate, central and local), and to distinguish each of the special bodies. In respect of each class of men concerned in the government we shall ask: How were they recruited? What was their official authority? What were their real powers? (2) What were the official rules? What was their form (custom, orders, law, precedent)? What was their content (rules of law)? What was the mode of application (procedure)? And, above all, how did the rules differ from the practice (abuse of power, exploitation, conflicts between executive agents, non-observance of rules)? After the determination of all the facts which constitute a society, it remains to find the place which this society occupies among the total number of the societies contemporary with it. Here we enter upon the study of international institutions, intellectual, economic, and political (diplomacy and the usages of war); the same questions apply as in the study of political institutions. A study should also be made of the habits common to several societies, and of those relations which do not assume an official form. This is one of the least advanced parts of historical construction. IV. The outcome of all this labour is a tabulated view of human life at a given moment; it gives us the knowledge of a _state_ of society (in German, _Zustand_). But history is not limited to the study of simultaneous facts, taken in a state of rest, to what we may call the _statics_ of society. It also studies the states of society at different moments, and discovers the differences between these states. The habits of men and the material conditions under which they live change from epoch to epoch; even when they appear to be constant they do not remain unaltered in every respect. There is therefore occasion to investigate these changes; thus arises the study of successive facts.