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Belief Revision: The Resubsumption Theory 353

which the person is already thinking about B or vice versa; and in other ways
as well. The person is now aware that he has two different ways of thinking
about B, in terms of Th(A) and in terms of Th(B), the former now being seen
as having a wider scope than previously thought and hence to be better charac-
terized as Th(A+B). If his background theory dictates that Th(A+B) and Th(B)
are incompatible, local coherence has been breached. The resubsumption of B
under Th(A+B) has made the latent conflict manifest.
The third process is conflict resolution through competitive evaluation.
Belief systems and informal theories are tools for dealing with the cognitive
tasks a person encounters in the course of life. A person’s confidence in a theory
will change as a result of his success or failure when that theory is applied. If the
learner’s cognitive ecology is such that he encounters frequent opportunities to
apply the two contending theories, he will gather information about their rela-
tive utility. Utility, in turn, drives confidence. If Th(A+B) is in fact a more useful
theory for domain B than Th(B), then experience will decrease his confidence
in the resident theory and increase his confidence in the contender theory.
Eventually, the two confidence levels will pass each other and the person finds
himself having greater confidence in the contender than in the resident theory.
The successes of the contender, not the failures of the resident theory, drive the
shift between the two theories. Figure 10.2 graphically illustrates the emergence
of a latent conflict, bisociation and competitive evaluation.
The fourth process is the switch in truth value, belief revision narrowly
construed. The theory claims that the two processes of adjusting confidence
and switching truth value are independent in the sense that there can be shifts
in confidence that are not accompanied by shifts in truth value. The theory
claims that the switch in truth value is a function of the relative levels of confi-
dence associated with the competing theories. If the confidence in the resident
theory continues to decrease and that of the contender theory to increase, the
cumulative consequence will be that the person finds himself believing the
latter.
The fifth process is the propagation of the truth value switch, a point
change, throughout the belief base. If the change in truth value is associated
with a single, peripheral belief, the change might be minor. If the altered belief
is a component of a belief system of large scope, the change might propagate
downward and upward through the belief base. If the propagation wave affects
many beliefs, the person might experience himself subjectively as undergoing
a significant change of mind, a conversion.
The five mechanisms of the theory – monotonic belief formation, biso-
ciation, competitive evaluation, truth value switch and propagation through