(1) A man writes a monograph when he proposes to elucidate a special point, a single fact, or a limited body of facts, for example the whole or a portion of the life of an individual, a single event or a series of events between two dates lying near together. The types of possible subjects of a monograph cannot be enumerated, for the subject-matter of history can be divided indefinitely, and in an infinite number of ways. But all modes of division are not equally judicious, and, though the reverse has been maintained, there are, in history as in all the sciences, subjects which it would be stupid to treat in monographs, and monographs which, though well executed, represent so much useless labour.[220] Persons of moderate ability and no great mental range, devoted to what is called "curious" learning, are very ready to occupy themselves with insignificant questions;[221] indeed, for the purpose of making a first estimate of an historian's intellectual power, a fairly good criterion may be had in the list of the monographs he has written.[222] It is the gift of seeing the important problems, and the taste for their treatment, as well as the power of solving them, which, in all the sciences, raise men to the first rank. But let us suppose the subject has been rationally chosen. Every monograph, in order to be useful--that is, capable of being fully turned to account--should conform to three rules: (1) in a monograph every historical fact derived from documents should only be presented accompanied by a reference to the documents from which it is taken, and an estimate of the value of these documents;[223] (2) chronological order should be followed as far as possible, because this is the order in which we know that the facts occurred, and by which we are guided in searching for causes and effects; (3) the title of the monograph must enable its subject to be known with exactitude: we cannot protest too strongly against those incomplete or fancy titles which so unnecessarily complicate bibliographical searches. A fourth rule has been laid down; it has been said "a monograph is useful only when it exhausts the subject"; but it is quite legitimate to do temporary work with documents which one has at one's disposal, even when there is reason to believe that others exist, provided always that precise notice is given as to what documents have been employed.