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The Formation of Belief 313

changes, conversion theorists inspired by science de-emphasize resistance
and focus primarily on successful conversions. However, resistance cannot be
ignored, and it makes the emergence of novel theories harder to understand.
A satisfactory explanation must describe the creation of novel theories but also
explain why encounters with contradictory information sometimes result in
conversion (acceptance of the contender theory) and sometimes in resistance
(continued acceptance of the resident theory). Theorists have proposed sev-
eral useful concepts and principles, but they do not add up to a satisfactory
account of conversion in response to contradictory information, whether in
science or in everyday life.

Progress Through Falsification

in the 19th century, philosophers of science emphasized the induction of gen-
eralities from data. But induction applies primarily to the initial stages of
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inquiry in a newly opened field of research. it does not explain what happens
when an already established theory encounters contradictory observations. in
his 1934 book Logic der Forschung, philosopher Karl Popper broke out of the
inductive view by arguing that a theory that is contradicted by data is falsi­
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fied. “[A scientific theory] is never inferred, in any sense, from the empirical
evidence. There is neither a psychological nor a logical induction. Only the
falsity of the theory can be inferred from empirical evidence, and this inference
is a purely deductive one.” A theory implies certain predictions about how the
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data from an investigation should turn out; if the predictions turn out to be
false, then the theory is false. in his view, falsification is a move from true(P)
to false (P) via a Modus Tollens inference

true (Th) implies true (o)
false (o)
so false (Th)
where “Th” stands for a theory and “o” refers to an observation, experimental
finding or the like. “… there is no more rational procedure than the method of trial
and error – of conjecture and refutation: of boldly proposing theories; of trying
our best to show that these are erroneous; and of accepting them tentatively if
our critical efforts are unsuccessful.” encounters with contradictory informa-
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tion drive science forward because they prompt scientists to abandon their theo-
ries and thereby prompt them to seek new and presumably better ones.
Popper was trying to solve the epistemological problem of scientific
progress: How can we be sure that scientific knowledge improves over time?