e one that will apply
perfectly to many other facts at present unknown. A hypothesis is a
great stimulus to the discovery of fresh facts. Science does not like
to have unverified hypotheses lying around loose, where they may trip
up the unwary. It is incumbent on any one who puts forward a
hypothesis to apply it to as many special cases as possible, in order
to see whether it works or not; and if the propounder of the
hypothesis is so much in love with it that he fails to give it a
thorough test, his scientific colleagues are sure to come to the
rescue, for they, on the whole, would be rather pleased to see the
other fellow's hypothesis come to grief. In this way, the rivalry
motive plays a useful part in the progress and stabilizing of science.

Deductive and Inductive Reasoning

When you are sure at the outset of your general proposition, and need
only to see its application to special cases, your reasoning is said
to be "deductive". Such reasoning is specially used in mathematics.
But in natural science you are said to employ "inductive reasoning".
The process has already been described. You start with particular
facts demanding explanation or generalization, and try to find some
accepted law that explains them. Failing in that, you are driven to
guess at a general law, i.e., to formulate a hypothesis that will fit
the known facts. Then, having found such a conjectural general law,
you proceed to deduce its consequences; you see that, _if_ the
hypothesis is true, such and such facts must be true. Next you go out
and see whether these facts are true, and if they are, your hypothesis
{475} is verified to that extent, though it may be upset later. If the
deduced facts are not true, the hypothesis is false, and you have to
begin all over again.

The would-be natural scientist may fail at any one of several points.
First, he may see no question that calls for investigation. Everything
seems a matter-of-course, and he concludes that science is complete,
with nothing left for him to discover. Second, seeing something that
still requires explanation, he may lack fertility in guessing, or may
be a poor guesser and set off on a wild-goose chase. Helmholtz, an
extremely fertile inventor of high-grade hypotheses, describes how he
went about it. He would load up in the morning with all the knowledge
he could assemble on the given question, and go out in the afternoon
for a leisurely ramble; when, without any strenuous effort