The operations of history are so numerous, from the first discovery of the document to the final formula of the conclusion, they require such minute precautions, so great a variety of natural gifts and acquired habits, that there is no man who can perform _by himself_ all the work on any one point. History is less able than any other science to dispense with the division of labour; but there is no other science in which labour is so imperfectly divided. We find specialists in critical scholarship writing general histories in which they let their imagination guide them in the work of construction;[185] and, on the other hand, there are constructive historians who use for their work materials whose value they have not tested.[186] The reason is that the division of labour implies a common understanding among the workers, and in history no such understanding exists. Except in the preparatory operations of external criticism, each worker follows the guidance of his own private inspiration; he is at no pains to work on the same lines as the others, nor does he pay any regard to the whole of which his own work is to form a part. Thus no historian can feel perfectly safe in adopting the results of another's work, as may be done in the established sciences, for he does not know whether these results have been obtained by trustworthy methods. The most scrupulous go so far as to admit nothing until they have done the work on the documents over again for themselves. This was the attitude adopted by Fustel de Coulanges. It is barely possible to satisfy this exacting standard in the case of little-known periods, the documents relating to which are confined to a few volumes; and yet some have gone so far as to maintain the dogma that no historian should ever work at second hand.[187] This, indeed, is what an historian is compelled to do when the documents are too numerous for him to be able to read them all; but he does not say so, to avoid scandal. It would be better to acknowledge the truth frankly. So complex a science as history, where facts must ordinarily be accumulated by the million before it is possible to formulate conclusions, cannot be built up on this principle of continually beginning afresh. Historical construction is not work that can be done with documents, any more than history can be "written from manuscripts," and for the same reason--the shortness of time. In order that science may advance it is necessary to combine the results of thousands of detail-researches.