thus ends by becoming a combination of features borrowed from different experiences.
It is not enough to represent to oneself isolated persons, objects, and actions. Men and their actions form part of a whole, of a society and of a process of evolution. It is, therefore, further necessary to represent to oneself the relations between different men and different actions (nations, governments, laws, wars).
But in order to imagine relations it is necessary to have a conception of collectivities or wholes, and the documents only give isolated elements. Here again the historian is obliged to use a subjective method. He imagines a society or a process of evolution, and in this imaginary framework he disposes the elements furnished by the documents. Thus, whereas biological classification is guided by the objective observation of physical units, historical classification can only be effected upon subjective units existing in the imagination.
The realities of the past are things which we do not observe, and which we can only know in virtue of their resemblance to the realities of the present. In order to realise the conditions under which past events happened, we must observe the humanity of to-day, and look for the conditions under which analogous events happen now. History thus becomes an application of the descriptive sciences which deal with humanity, descriptive psychology, sociology or social science; but all these sciences are still but imperfectly established, and their defects retard the establishment of a science of history.
Some of the conditions of human life are, however, so necessary and so obvious that the most superficial observation is enough to establish them. These are the conditions common to all humanity; they have their origin either in the physiological organisation which