study. Deductive reasoning is the way in which predictions are used
to test a hypothesis.Testing
In the twentieth century, philosopher Karl Popper introduced the idea
that a hypothesis must be falsifiable; that is, it must be capable of being
demonstrated wrong. A hypothesis must make specific predictions;
these predictions can be tested with concrete measurements to support
or refute the hypothesis. For instance, Albert Einstein’s theory of gen-
eral relativity makes a few specific predictions about the structure of
space and flow of time, such as the prediction that light bends in a
strong gravitational field, and the amount of bending depends in a pre-
cise way on the strength of the gravitational field. Observations made
of a 1919 solar eclipse supported this hypothesis against other possi-
ble hypotheses, such as Sir Isaac Newton’s theory of gravity, which did
not make such a prediction. British astronomers used the eclipse to
prove Einstein’s theory and therefore, eventually replaced Newton’s
theory.Verification
Probably the most important aspect of scientific reasoning is verifi-
cation. Verification is the process of determining whether the
hypothesis is in accord with empirical evidence, and whether it will
continue to be in accord with a more generally expanded body of evi-
dence. Ideally, the experiments performed should be fully described
so that anyone can reproduce them, and many scientists should inde-
pendently verify every hypothesis. Results that can be obtained from
experiments performed by many are termed reproducibleand are
given much greater weight in evaluating hypotheses than non-repro-
ducible results.Evaluation
Falsificationism argues that any hypothesis, no matter how respected
or time-honored, mustbe discarded once it is contradicted by new reli-
able evidence. This is, of course, an oversimplification, since individ-
ual scientists inevitably hold on to their pet theory long after contrary
evidence has been found. This is not always a bad thing. Any theory
can be made to correspond to the facts, simply by making a few adjust-
ments—called “auxiliary hypothesis”—so as to bring it into corre-
spondence with the accepted observations. The choice of when to
reject one theory and accept another is inevitably up to the individual
scientist, rather than some methodical law.(35)
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