form nearly the whole of our knowledge of social life. Now, the greater part of these are to some extent false, for the science of social life is still imperfect. And the chief danger in them lies in the circumstance that we use them unconsciously. The safest precaution will be always to formulate the supposed law on which we propose to base an argument. In every instance where such and such a fact occurs, it is certain that such and such another fact occurs also. If this proposition is obviously false, we shall at once see it to be so; if it is too general, we shall inquire what new conditions may be introduced to make it accurate.
(2) A second spontaneous impulse leads us to draw consequences from isolated facts, even of the slightest kind (or rather, the idea of each fact awakens in us, by association, the idea of other facts). This is the natural procedure in the history of literature. Each circumstance in the life of an author supplies material for reasoning; we construct by conjecture all the influences which could have acted upon him, and we assume that they did act upon him. All the branches of history which study a single species of facts, isolated from every other species (language, arts, private law, religion), are exposed to the same danger, because they deal with fragments of human life, not with comprehensive collections of phenomena. But few conclusions are firmly established except those which rest on a comprehensive body of data. We do not make a diagnosis from a single symptom, but from a number of concurrent symptoms. The precaution to be taken will be to avoid working with an isolated detail