I have been asked to write an article explaining “just how a source book is to be used, its relation to the text-book, the kind of information and the kind of training a careful teacher can impart through it and the advantage it offers over the exclusive use of secondary material.” Instead of answering the whole question and treating of all the uses of the source book, it seemed wise to treat but one, the most characteristic use to which the sources could be put, namely, the critical study of sources as evidence, for the purpose of training the pupil in the methods of historical proof. The importance that I attach to this matter of method is due to my conception of educational theory and of the logic of historical science. About this broader basis upon which the teaching of history must rest, it may be well to say a word by way of preface. Method the Object Sought. Personally I am in hearty sympathy with the new educational theory that attributes more importance to method than to matter. Professor Lanson, of the University of Paris, the distinguished historian of French literature, has given so satisfactory a formulation of the aims of this theory in its application to secondary education that I cannot do better than reproduce his statement.[1] “Now it is necessary,” he writes, “to prove that what we need to-day is minds scientifically trained. Let us understand by this word (scientifically) that sounds so ambitious, minds that have the taste or the sense for the true, that carry into all their actions a serious desire for clear and exact knowledge, that are conscious of the difficulties and dangers that one encounters in the pursuit of or in the elaboration of truth, that distrusting everybody, themselves as well as others, take all the precautions indicated in each case in order not to deceive themselves or to be deceived: these precautions are what we call methods. _The methodical search for truth?_ There, in a word, is what the scientific spirit means and to make it dominate in secondary education is to subordinate all studies to the idea that their common end, their convergent directions ought to be to fashion minds that all their lives, in all things will know how to practice the methodical search for truth.... In every study and exercise, the aim of the master ought to be to develop in the minds of his pupils the sense and the taste for truth, to cause them to note how in each subject the truth is found or missed, to put them, finally, in possession of a certain method or discipline appropriate to a certain object. It is not a matter of having them learn a large number of laws or facts, but, by well-chosen examples, to learn what a mathematical truth is and how it is elaborated; likewise a chemical truth, a physiological truth, an astronomical truth and a historical truth. How does each of these truths of different orders come into existence? By what means does it separate itself from other truths? What are the signs by which