Let us take our example from political science. The historical method, in its popular sense, has been so much used here, even to the exclusion of other methods, that it would seem needless to speak of it. But often the method has been abused and often it has not been given broad enough treatment. It traces the growth of an institution, or of an idea—personal liberty, say,—through successive periods. It notes what the path has been, and judges of the probable future tendency. But a far broader outlook than we get from this narrowly conceived “historical” method is furnished by evolutionary sociology. Here we inquire into the origin of society and of the various trades, industries, professions and pursuits of all kinds, and to do this we go far into prehistoric times. Nowhere is the evolutionary method more strikingly seen than in biology. Since Darwin’s great theory was promulgated the science has gone forward by leaps and bounds. We have derived untold benefit from a comparison of man and animals in the light of this hypothesis; even study of the development of individual man has been aided. The discovery of the _fact_ of evolution constituted an incalculable advance, but the method for study which it furnished was of even greater importance. I have spoken of the comparison of man and animals “in the light of this (evolutionary) hypothesis.” This brings us to a point which must be kept in mind in practically all observation. We are often exhorted to “observe.” Presumably we are to do this “on general principles.” Such advice is about as foolish as asking us to think on general principles. Imagine for the moment what would happen if you started right now to “observe” as much as you could. You might begin with this book and notice the size of the type, the amount of margin, the quality of the paper, the dimensions of the page, the number of pages. But you have by no means exhausted the number of properties possessed by this book. You must observe that it is also combustible, that it is destructible, that it is machine made, that it is American printed, that it is such and such a price, that it weighs so many ounces, that it is flat, that it is rectangular, that its thickness is so much. . . . The absurdity is obvious. If we started out merely to observe, with no definite purpose in mind, we could keep it up forever. And get nowhere. Nine out of every ten observations would never be put to use. We would be sinfully wasting our time. To observe most profitably, just as to think most profitably, we must have a definite purpose. This purpose must be _to test the truth of a supposition_. A concrete example will make this clear.