Generics, Frequency Adverbs, and Probability

only world open to our inspection is the actual one, but under any reasonable
conception of normality, the actual world is not normal. How, then, can
we tell what things are like in a normal world? And how can we judge the
truth values of generics and frequency statements, if such judgments require
knowledge of normal worlds?
Admissible histories, in contrast with normal worlds, are not opaque.
While it is true that admissible histories cannot be observed in their entirety
in the actual world, we are in a position to observe their initial segment,
since all admissible histories continue the relevant part of the actual history.
Thus, the longer the relevant actual history, the more information we have
regarding the admissible histories, and the more confidence we have in extrapolating
their properties. This approach provides a direct link between
observations in the actual world and the truth judgments of generics and frequency
statements: while not completely determining such truth judgments,
observations in the actual world help us extrapolate to admissible histories,
with respect to which we make our truth judgments. No such link is provided
by theories which propose that generics and frequency statements are
expressions of normality.
The only requirement from an admissible history is that it continue a
regularity observed throughout a sufficiently long sample in the actual world.
In particular, we need not postulate any rules or laws which hold in an
admissible history. Presumably, an observed regularity does follow from some
rule, be it physical, social, genetic, or whatever; but importantly, we need
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