In the case of antiquity and the middle ages historical knowledge is limited to general facts by the scarcity of documents. In dealing with contemporary history it is possible to include more and more particular facts. The general public supposes the opposite of this; it is suspicious about contemporary facts, with reference to which it sees contradictory narratives circulating, and believes without hesitation ancient facts, which it does not see contradicted anywhere. Its confidence is at its greatest in respect of that history which we have not the means of knowing, and its scepticism increases with the means of knowledge. VI. _Agreement between documents_ leads to conclusions which are not all of them definitive. In order to complete and rectify our conclusions we have still to study _the harmony of the facts_. Several facts which, taken in isolation, are only imperfectly proved, may confirm each other in such a manner as to produce a collective certainty. The facts which the documents present in isolation have sometimes been in reality sufficiently near each other to be connected. Of this kind are the successive actions of the same man or of the same group of men, the habits of the same group at different epochs separated by short intervals, or of similar groups at the same epoch. It is no doubt possible that one of several analogous facts may be true and another false; the certainty of the first does not justify the categorical assertion of the second. But yet the harmony of several such facts, each proved imperfectly, yields a kind of certainty; the facts do not, in the strict sense of the word, prove, but they _confirm_[175] each other. The doubt which attached to each one of them disappears; we obtain that species of certainty which is produced by the interconnection of facts. Thus the comparison of conclusions which are separately doubtful yields a whole which is morally certain. In an itinerary of a sovereign, the days and the places confirm each other when they harmonize so as to form a coherent whole. An institution or a popular usage is established by the harmony of accounts, each of which is no more than probable, relating to different times and places.