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The Formation of Belief 297

experimental finding, especially not a finding from some other researcher’s
laboratory. Louis Pasteur’s hypothesis that micro-organisms are involved in
fermentation, the out-of-Africa theory of the human colonization of the earth
and the atomic disintegration theory of radioactivity developed by, among
others, J. J. Thompson, ernest rutherford and Frederick soddy are only three
11
of the many advances in science that were resisted by scientists at the time.
Unlike a logical theory, a psychological theory of belief revision must explain
the nature and mechanism of resistance. in the words of Thomas s. Kuhn: “We
must … ask how conversion is induced and how resisted.” 12
resistance does not prevent conversions, but it makes them more difficult
to explain. A theory of non-monotonic belief revision cannot limit itself to
describe the processes by which new beliefs are created. it must also explain
why contradictory information triggers conversion in some cases but resis-
tance in others.
To summarize, a theory of conversion must answer two interlocked sets
of questions: First, how, by what processes, is change resisted? if a person does
not respond to contradictory information by revising his beliefs, how does he
respond? second, how, by what processes, and when, under which conditions,
is resistance overcome and beliefs revised? A theory of conversion that lacks
an account of resistance implicitly predicts that conversion is the common
and unproblematic consequence of encounters with contradictory informa-
tion, while a theory that only specifies the mechanisms of resistance implicitly
predicts that conversions never happen. it is possible to explain resistance and
conversion by postulating two different processes that produce the two differ-
ent outcomes, but such dual-process theories require some mechanism that
causes a switch between the two. A more elegant theory explains resistance and
revision as alternative outcomes of one and the same cognitive mechanism.
Furthermore, a theory of conversion needs to specify the factors that determine
the direction of a conversion process. Given a large belief base, there are infi-
nitely many possible revisions; which one will occur in each particular case?
Cognitive psychologists, educational researchers, logicians, philosophers
of science and social scientists have contributed useful concepts and partial
answers to these questions. in the next section i weave those contributions
into a theory of resistance to cognitive change in the face of contradictory
information. i then review the conversion mechanisms inspired by the his-
tory of theory change in science and argue that they fail to explain how
resistance is overcome. The strength and weaknesses of the prior theoretical
proposals point the way to the rather different theory of conversion proposed
in Chapter 10.