A natural instinct leads us to judge of the value of statements by their form. We think we can tell at a glance whether an author is sincere or a narrative accurate. We seek for what is called "the accent of sincerity," or "an impression of truth." This impression is almost irresistible, but it is none the less an illusion. There is no external criterion either of good faith or of accuracy. "The accent of sincerity" is the appearance of conviction; an orator, an actor, an habitual liar will put more of it into his lies than an undecided man into his statement of what he believes to be the truth. Energy of affirmation does not always mean strength of conviction, but sometimes only cleverness or effrontery.[147] Similarly, abundance and precision of detail, though they produce a vivid impression on unexperienced readers, do not guarantee the accuracy of the facts;[148] they give us no information about anything but the imagination of the author when he is sincere, or his impudence when he is the reverse. We are apt to say of a circumstantial narrative: "Things of this kind are not invented." They are not invented, but they are very easy to transfer from one person, country, or time to another. There is thus no external characteristic of a document which can relieve us of the obligation to criticise it. The value of an author's statement depends solely on the conditions under which he performed certain mental operations. Criticism has no other resource than the examination of these conditions. But it is not a case of reconstructing all of them; it is enough to answer a single question: did the author perform these operations correctly or not? The question may be approached on two sides.