indispensable precaution in dealing with large totals in statistics and descriptions of popular usages; for it is possible that the author may have obtained the total he gives by a process of conjectural valuation (this is the ordinary practice in stating the number of combatants or killed in a battle), or by combining subsidiary totals, all of which were not accurate; it is possible that he may have extended to a whole people, a whole country, a whole period, that which was true only of a small group known to him.
VI. These two first series of questions bearing on the good faith and the accuracy of the statements in the document are based on the supposition that the author has observed the fact himself. This is a feature common to all reports of observations in the established sciences. But in history there is so great a dearth of direct observations, of even moderate value, that we are obliged to turn to account documents which every other science would reject. Take any narrative at random, even if it be the work of a contemporary, it will be found that the facts observed by the author are never more than a part of the whole number. In nearly every document the majority of the statements do not come from the author at first hand, but are reproductions of the statements of others. Even where a general relates a battle in which he commanded, he does not communicate his own observations, but those of his officers; his narrative is in a large measure a "second-hand document."
In order to criticise a second-hand statement it is no longer enough to examine the conditions under which the author of the