have lied; what he believed is not necessarily what happened, for he may have been mistaken. These propositions are obvious. And yet a first and natural impulse leads us to accept as true every statement contained in a document, which is equivalent to assuming that no author ever lied or was deceived; and this spontaneous credulity seems to possess a high degree of vitality, for it persists in spite of the innumerable instances of error and mendacity which daily experience brings before us.
Reflection has been forced on historians in the course of their work by the circumstance of their finding documents which contradicted each other; in such cases they have been obliged to doubt, and, after examination, to admit the existence of error or mendacity; thus negative criticism has appeared as a practical necessity for the purpose of eliminating statements which are obviously false or erroneous. But the instinct of confidence is so indestructible that it has hitherto prevented even those professionally concerned from systematising the internal criticism of statements in the same way as the external criticism which deals with the origin of documents has been systematised. Historians, in their works, and even theoretical writers on historical method, have been satisfied with common notions and vague formulæ in striking contrast with the precise terminology of the critical investigation of sources. They are content to examine whether the author was roughly contemporary with the events, whether he was an ocular witness, whether he was sincere and well-informed, whether he knew the truth and desired to tell it, or even—summing up the whole question in a single formula—whether he was trustworthy.
This superficial criticism is certainly better than no criticism at all, and has