extend to this intellectual analysis of subjective impressions the rules which govern the real analysis of real objects.
History, then, must guard against the temptation to imitate the method of the biological sciences. Historical facts are so different from the facts of the other sciences that their study requires a different method.
III. Documents, the sole source of historical knowledge, give information on three categories of facts:
(1) Living beings and material objects. Documents make us acquainted with the existence of human beings, physical conditions, products of art and industry. In all these cases physical facts have been brought before the author by physical perception. But we have before us nothing but intellectual phenomena, facts seen "through the author's imagination," or, to speak accurately, mental images representative of the author's impressions—images which we form on the analogy of the images which were in his mind. The Temple at Jerusalem was a material object which men saw, but we cannot see it now; all we can now do is to form a mental image of it, analogous to that which existed in the minds of those who saw and described it.
(2) Actions of men. Documents relate the actions (and words) of men of former times. Here, too, are physical facts which were known to the authors by sight and hearing, but which are now for us no more than the author's recollections, subjective images which are reproduced in our minds. When Cæsar was stabbed the dagger-thrusts were seen, the words of the murderers were heard; we have nothing but mental images. Actions and words all have this characteristic, that each was the action or the word of an individual; the imagination can only represent to itself individual