A little reflection, however, will relieve us from this perplexity, and assure us that the alleged analogy between the comparison of words and the comparison of stories is utterly superficial. The transformations of words--which are often astounding enough--depend upon a few well-established physiological principles of utterance; and since philology has learned to rely upon these principles, it has become nearly as sure in its methods and results as one of the so-called "exact sciences." Folly enough is doubtless committed within its precincts by writers who venture there without the laborious preparation which this science, more than almost any other, demands. But the proceedings of the trained philologist are no more arbitrary than those of the trained astronomer. And though the former may seem to be straining at a gnat and swallowing a camel when he coolly tells you that violin and fiddle are the same word, while English care and Latin cura have nothing to do with each other, he is nevertheless no more indulging in guess-work than the astronomer who confesses his ignorance as to the habitability of Venus while asserting his knowledge of the existence of hydrogen in the atmosphere of Sirius. To cite one example out of a hundred, every philologist knows that s may become r, and that the broad a-sound may dwindle into the closer o-sound; but when you adduce some plausible etymology based on the assumption that r has changed into s, or o into a, apart from the demonstrable influence of some adjacent letter, the philologist will shake his head.
Now in the study of stories there are no such simple rules all cut and dried for us to go by. There is no uniform psychological principle which determines that the three-headed snake in one story shall become a three-headed man in the next. There is no Grimm's Law in mythology which decides that a Hindu magician shall always correspond to a Norwegian Troll or a Keltic Druid. The laws of association of ideas are not so simple in application as the laws of utterance. In short, the study of myths, though it can be made sufficiently scientific in its methods and results, does not constitute a science by itself, like philology. It stands on a footing similar to that occupied by physical geography, or what the Germans call "earth-knowledge." No one denies that all the changes going on over the earth's surface conform to physical laws; but then no one pretends that there is any single proximate principle which governs all the phenomena of rain-fall, of soil-crumbling, of magnetic variation, and of the distribution of plants and animals. All these things are explained by principles obtained from the various sciences of physics, chemistry, geology, and physiology. And in just the same way the development and distribution of stories is explained by the help of divers resources contributed by philology, psychology, and history. There is therefore no real analogy between the cases cited by Max Muller. Two unrelated words may be ground into exactly the same shape, just as a pebble from the North Sea may be undistinguishable from another pebble on the beach of the Adriatic; but two stories like those of Punchkin and the Heartless Giant are no more likely to arise independently of each other than two coral reefs on opposite sides of the globe are likely to develop into exactly similar islands.
Shall we then say boldly, that close similarity between legends is proof of kinship, and go our way without further misgivings? Unfortunately we cannot dispose of the matter in quite so summary a fashion; for it remains to decide what kind and degree of similarity shall be considered satisfactory evidence of kinship. And it is just here that doctors may disagree. Here is the point at which our "science" betrays its weakness as compared with the sister study of philology.
