The work of criticism has supplied us with nothing but a number of isolated remarks on the value of the knowledge which the documents have permitted us to acquire. These must be combined. We shall therefore take a whole group of facts entered under a common heading--a particular class of facts, a country, a period, an event--and we shall summarise the results yielded by the criticism of particular facts so as to obtain a general formula. We shall have to take into consideration: (1) the extent, (2) the value of our knowledge. (1) We shall ask ourselves what are the blanks left by the documents. By working through the scheme used for the grouping of facts it is easy to discover what are the classes of facts on which we lack information. In the case of evolution, we notice which links are missing in the chain of successive modifications; in the case of events, what episodes, what groups of actors are still unknown to us; what facts enter or disappear from the field of our knowledge without our being able to trace their beginning or end. We ought to construct, mentally at any rate, a tabulated scheme of the points on which we are ignorant, in order to keep before our minds the distance separating the knowledge we have from a perfect knowledge. (2) The value of our knowledge depends on the value of our documents. Criticism has given us indications on this point in each separate case, these indications, so far as relating to a given body of facts, must be summarised under a few heads. Does our knowledge come originally from direct observation, from written tradition, or from oral tradition? Do we possess several traditions of different bias, or a single tradition? Do we possess documents of different classes or of one single class? Is our information vague or precise, detailed or summary, literary or positive, official or confidential?