The problem should have been selected by the teacher, as one easy of solution, the trap laid and the class led into it. The texts disagree; which states the truth? Who wrote the texts? Suppose the event treated is from the French Revolution. How did the writers know anything about it? What were their sources? How could we find out what actually happened a century ago? Evidently through the records made by witnesses of the events. Have we any such on this topic and who are they? This question may be answered by the teacher, who might put the sources into the hands of the pupils, or a simple problem in bibliography might be set the class and the exercise postponed until the next meeting. Let the pupils bring into the class the statement of at least one man who, they assume, knew something about this event. Take up these sources in turn. How do the pupils know that this account was really written by this man? (Genuineness.) How do they know that the man really knew anything about the event? (Localization.) How do they know that he made a correct record of what he saw? (Value of the source, based on perception and memory.) Even if the man is a good witness, does his unsupported statement (affirmation) prove the fact? Dwell on the possibilities of error; show that even if he wishes to tell the truth, no man can be certain that his uncontrolled memory is not playing him false or that he saw the thing correctly in the first place. Will the agreement of two witnesses be sufficient to give us certainty? Show that this is true only when the witnesses are independent of each other. In the problem taken up by the class, are there two or more independent witnesses? Is the fact upon which the school texts disagree settled by the agreement of two independent witnesses? If so, why do the texts disagree? It may be due to the fact that each writer used but one source, and that the statement in that source was incorrect, or the witnesses may disagree and one writer may have accepted one statement, the other another. If the conclusions are not equally probable, try to show on which side the weight of probability lies. Point out, further, in conclusion, that where we are not certain as to what happened--where the witnesses disagree--we have only probability, not certainty, and the secondary text ought to make this clear. Pupils Handling Sources.