Thinking and Deciding

HYPOTHESES IN SCIENCE 165
disease, we conclude that the disease is not bacterial, yet the bacterium in question
may turn out to be an oddity, a type that can withstand high temperature.
In the early stages of scientific inquiry, scientists must stumble around in the
dark, using methods that are still untested in order to establish facts, which, if they
are established, validate the methods themselves.
Testing scientific hypotheses
Much of the literature in the philosophy of science is concerned with the normative
and prescriptive theory of hypothesis formulation and testing. In science, hypotheses
are often derived from theories, which are coherent explanations of several different
phenomena. Newton’s theory of gravitation, for example, explains the motions of
the moon and the planets, and the trajectories and acceleration of bodies in free fall
near the earth. A new hypothesis derived from this theory is that gravitational force
is reduced at the tops of mountains.
The work of Karl Popper has had an especially important influence on our thinking
about theories and how they are tested (see Popper, 1962, especially ch. 1). Popper
wanted to carry out a “rational reconstruction” of scientific practice: That is, he
wanted to look at the actual practice of scientists and describe it in the most “charitable”
way. He assumed that scientists were often rational, and he tried to use this
assumption to discover the nature of rationality in science.
Popper was particularly interested in trying to distinguish the method of formulating
theories in the more successful sciences, such as modern physics (especially
Einstein’s theory of relativity), from the method used in what he considered questionable
sciences, including the psychoanalytic theories of Adler (for whom Popper
had worked for a time) and Freud and the political theory of Marx. Popper criticized
these latter theories for their apparent capacity to explain any result or observation.
When some Freudians or Marxists were given counterexamples to their favored theories,
he said, they always had some explanation of why the counterexample was not
a good one. At worst, they would accuse their critic of bias, terming it “resistance”
or “false consciousness.”
In contrast, Popper noted, Einstein’s theory of relativity made a strong prediction
about the exact angle at which a beam of starlight would be bent as it passed by the
sun. If the angle had been anything other than predicted, Einstein would have had
to admit that his theory was incorrect, but the prediction was accurate. Einstein’s
theory, in contrast to Freud’s or Marx’s, was therefore falsifiable — that is, capable
of being proved false by an experiment or observation. Moreover, Einstein’s theory
was a great advance, because the prediction was risky: In terms of the other theories
accepted at that time, the angle that Einstein’s theory predicted was considered
extremely unlikely.
Popper therefore concluded that sciences advance successfully by making theoretical
statements that are “bold conjectures” and then trying to refute them (falsify
them) through experiment or observation. Those conjectures that survive the attempts
to refute them become accepted theories, such as the theory of relativity, but