Here, then, we have the future historian armed with the preliminary knowledge, the neglect of which would have condemned him to powerlessness or to continual mistakes. We suppose him protected from the errors without number which have their origin in an imperfect knowledge of the writing and the language of documents, in ignorance of previous work and the results obtained by textual criticism; he has an irreproachable _cognitio cogniti et cognoscendi_. A very optimistic supposition, by the way, as we are bound to admit. We know but too well that to have gone through a regular course of "auxiliary sciences," or to have read attentively the best treatises on bibliography, palæography, philology, and so on, or even to have acquired some personal experience by practical exercises, is not enough to ensure that a man shall always be well informed, still less to make him infallible. In the first place, those who have for a long time studied documents of a given class or of a given period possess, in regard to these, incommunicable knowledge in virtue of which they are able to deal better than others with new documents which they may meet with of the same class or period; nothing can replace the "special erudition" which is the specialist's reward for hard work.[53] And secondly, specialists themselves make mistakes: palæographers must be perpetually on their guard not to decipher falsely; is there a philologist who has not some faults of construing on his conscience? Scholars usually well informed have printed as unedited texts which had already been published, and have neglected documents it was their business to know. Scholars spend their lives in incessantly perfecting their "auxiliary" knowledge, which they rightly regard as never perfect. But all this does not prevent us from maintaining our hypothesis. Only let it be understood that in practice we do not postpone work upon documents till we shall have gained a serene and absolute mastery over all the "auxiliary branches of knowledge:" we should never dare to begin. It remains to know how to treat documents supposing one has successfully passed through the preliminary apprenticeship. BOOK II ANALYTICAL OPERATIONS CHAPTER I GENERAL CONDITIONS OF HISTORICAL KNOWLEDGE We have already stated that history is studied from documents, and that documents are the traces of past events.[54] This is the place to indicate the consequences involved in this statement and this definition.