I. Every conception which is expressed in writing or by any illustrative representation is in itself a definite, unimpeachable fact That which is expressed must have first been present in the mind of some one--if not in that of the author, who may have reproduced a formula he did not understand, then in the mind of the man who originated the formula. The existence of a conception may be learnt from a single instance and proved from a single document. Analysis and interpretation are thus sufficient for the purpose of drawing up the complete list of those facts which form the basis of the history of the arts, the sciences, or of doctrines.[167] It is the task of external criticism to localise these facts by determining the epoch, the country, the author of each conception. The duration, geographical distribution, origin, and filiation of conceptions belong to historical synthesis. Internal criticism has nothing to do here; the fact is taken directly from the document. We may advance a step farther. In themselves conceptions are nothing but facts in psychology; but imagination does not create its objects, it takes the elements of them from reality. Descriptions of imaginary facts are constructed out of the real facts which the author has observed in his experience. These elements of knowledge, the raw material of the imaginary description, may be sought for and isolated. In dealing with periods and with classes of facts for which documents are rare--antiquity, for example, and the usages of private life--the attempt has been made to lay under contribution works of literature, epic poems, novels, plays.[168] The method is legitimate, but only within the limits of certain restrictions which one is very apt to forget. (1) It does not apply to social facts of a psychological order, the moral or artistic standards of a society; the moral and æsthetic conceptions in a document give at most the individual standards of the author; we have no right to conclude from these to the morals or the æsthetic tastes of the age. We must at least wait till we have compared several different authors of the same period. (2) Descriptions even of physical facts and objects may be products of the author's imagination. It is only the _elements_ of them which we know to be certainly real; all that we can assert is the separate existence of the irreducible elements, form, material, colour, number. When the poet speaks of golden gates or silver bucklers, we cannot infer that golden gates and silver bucklers ever existed in reality; nothing is certain beyond the separate existence of gates, bucklers, gold, and silver. The analysis must therefore be carried to the point of distinguishing those elements which the author must necessarily have taken from experience: objects, their purpose, ordinary actions.