Critical scholars, who are accustomed to collect all the facts relating to their speciality, without any personal preference, are inclined to regard a complete, accurate, and objective collection of facts as the prime requisite. All historical facts have an equal right to a place in history; to retain some as being of greater importance, and reject the rest as comparatively unimportant, would be to introduce the subjective element of choice, variable according to individual fancy; history cannot sacrifice a single fact. Against this very reasonable view there is nothing to be urged except a material difficulty; this, however, is enough, for it is the practical motive of all the sciences: we mean the impossibility of acquiring or communicating complete knowledge. A body of history in which no fact was sacrificed would have to contain all the actions, all the thoughts, all the adventures of all men at all times. It would form a total which no one could possibly make himself master of, not for want of materials, but for want of time. This, indeed, applies, as things are, to certain voluminous collections of documents: the collected reports of parliamentary debates contain the whole history of the various assemblies, but to learn their history from these sources would require more than a lifetime. Every science must take into consideration the practical conditions of life, at least so far as it claims to be a real science, a science which it is possible to know. Any ideal which ends by making knowledge impossible impedes the establishment of the science. Science is a saving of time and labour, effected by a process which provides a rapid means of learning and understanding facts; it consists in the slow collection of a quantity of details and their condensation into portable and incontrovertible formulæ. History, which is more encumbered with details than any other science, has the choice between two alternatives: to be complete and unknowable, or to be knowable and incomplete. All the other sciences have chosen the second alternative; they abridge and they condense, preferring to take the risk of mutilating and arbitrarily combining the facts to the certainty of being unable either to understand or communicate them. Scholars have preferred to confine themselves to the periods of ancient history, where chance, which has destroyed nearly all the sources of information, has freed them from the responsibility of choosing between facts by depriving them of nearly all the means of knowing them. History, in order to constitute itself a science, must elaborate the raw material of facts. It must condense them into manageable form by means of descriptive formulæ, qualitative and quantitative. It must search for those connections between facts which form the ultimate conclusions of every science.