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as many fragments as possible must be collected, and even then no certain result might be reached.

Knowledge of the laws alone does not ordinarily suffice, and even if that knowledge were complete it might be possible to go astray in applying it. The greatest scientist might fail in the attempt to give a specific explanation of a concrete fact if he should overlook the circumstances surrounding the fact. Specific explanation is a matter for the application of science, and theory alone is proverbially insufficient as a guide for practice, no matter how correct the theory may be in the abstract. The "theorist " may have an incorrect theory or he may fail to note the special circumstances in applying one which is correct.

Closely related to the processes of explanation are those of prediction. They are complementary. In explaining, we give the laws and circumstances which account for a fact or a supposed fact; in prediction we set out from a set of laws and circumstances and attempt to show that a certain fact will occur in the future or will be found on further investigation to exist. Successful prediction is, as we have seen in studying the inductive methods, a test of the validity of the laws we are employing. If we do not know the laws and circumstances we can not predict successfully, except occasionally and by accident. Prediction may be said to represent the practical application of science.

CHAPTER II

HYPOTHESIS

What is an Hypothesis?-Before we go on to the discussion of certain typical systems, it is necessary to give some attention to another matter involved in most explanations, namely, the use of hypotheses. The term hypothesis is used in several different senses, but for our purposes an hypothesis is a provisional explanation. Fictions made for the purpose of argument, illustration, or simplification may also be regarded as hypotheses, but we shall use the term in the narrower sense.1

Hypotheses, or provisional explanations, may assert the existence of a fact, as when we assume that a defective flue was the cause of a fire; or of a law, as when we infer a causal connection between vaccination and freedom from smallpox; or of a complex system of laws and facts, as when we infer the existence of a matriarchal system in the early history of certain peoples. Inductive inferences, which were discussed in chapter vi., would fall under the head of hypotheses.

The Value of Hypotheses.-There has been much disagreement regarding the value of hypotheses and their use in science. A good many scientists have declared that hypotheses are not only unnecessary but

1 For an interesting discussion of the subject, see Muirhead, Philosophy and Life, Art. “ Hypothesis."

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are positively harmful, and Newton's "Hypotheses non fingo" is often quoted in defense of their position. To apply this literally would mean that a science would remain merely a body of carefully observed and classified facts, unless laws should somehow or other spring ready made from them without having been previously put forward as possible laws and then tested by further observation and experiment. Now, it might sometimes be possible to collect our facts over a very wide range and classify them and their relations in such a way as to show at once the law of their connections; the inductive methods indicate the sort of grouping that would be necessary; but even with their assistance it would rarely happen that a fully verified law would appear without previous unsuccessful attempts at its discovery. Previous to the Nineteenth Century the progress of science was seriously retarded by what Romanes has called the Bugbear of Speculation. In the introduction to his Darwin and after Darwin he gives the following statement of the situation in the natural sciences: "Fully awakened to the dangers of web-spinning from the ever fertile resources of their own inner consciousness, naturalists became more and more convinced that their science ought to consist in a mere observation of facts, or tabulation of phenomena without attempt at theorization upon their philosophical import. If the facts and phenomena presented any such import, that was an affair of the man of letters to deal with; but as men of science, it was their duty to avoid the seductive temptations of the world, the flesh and the devil, in the form of speculation, deduction, and generalization this was the

orthodox and general view." It was current in the time of Linnæus and even to the time of Cuvier. "The Origin of Species made an epoch . . . Darwin displayed the true principle which ought to govern biological research . . . he never loses sight of the distinction between fact and theory . . . but his idea of the scientific use of facts is plainly that of furnishing legitimate material for the construction of theories

the spirit of speculation is the same as the spirit of science, namely, to know the causes of things. If it be causes or principles as distinguished from facts or phenomena, that constitute the final aim of scientific research, obviously the advancement of such research can be attained only by the framing of hypotheses. And to frame such hypotheses is to speculate." Darwin said of himself that he made an hypothesis on every subject. "He was as productive of hypotheses as nature is of living things, and like her, he subjected them all to the principle of natural selection." 2

Hypotheses are necessary for science. "All science starts with hypotheses, in other words, with assumptions that are unproved, while they may be and often are erroneous; but which are better than nothing to the seeker after order in the maze of phenomena.” 3

An erroneous hypothesis may be quite as effective. in the field of practical activity as a true one could be. "The theory that some god would destroy the tribe if it did not wash at a particular time was a very crude explanation of an observed fact; but it nevertheless has its merits. It caused the tribe to wash occasionally

2 Cramer, The Method of Darwin, p. 40. 3 Huxley, Hume, p. 65.

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a thing it would never have done. It furnished a theory which tended to prevent disease. It recognized the truth which bacteriological science has only just grown up to in the present generation: that the penalty for violation of law was visited not so much on the individual as on the community.*

The Ptolemaic System was an erroneous hypothesis, but without it, or some other theory, astronomical knowledge would have progressed much more slowly than it did. "The superiority of the Greeks to their Oriental neighbors in science has often been accounted for by their fertility in theory. The Oriental peoples were, at the time of which we write (Cosmological Period), considerably richer than the Greeks in accumulated facts, though these facts had certainly not been observed for any scientific purpose, and their possession never suggested a revision of the primitive view of the world." 5

We

The danger in using hypotheses lies in the fact that we are so likely to forget that they are only hypotheses. We find some explanation which seems to fit the facts or which supports some other belief of ours, and we forget that our hypothesis has not been verified. tend to have too great a fondness for hypotheses which we have ourselves made; we are liable to "the partiality of intellectual parentage." Darwin's example may again be cited as the right one. "I have steadily endeavored to keep my mind free so as to give up any hypothesis, however much beloved (and I cannot resist

4 President Hadley, in an article in the Atlantic Monthly, February, 1903, p. 153.

5 Burnet, Early Greek Philosophy, 1st Ed., p. 22.