Generics, Frequency Adverbs, and Probability

though the truth conditions do depend on the extensions of the properties
at different times.
To give another example, suppose that John fears all bats but no other
animal. The set of bats is equivalent to the set of animals John fears, though
the intensions of the respective terms differ; there are any number of possible
worlds where John does not fear bats in the slightest.
However, we can
substitute the term animals which John fears for bats without changing the
truth conditions:
(9) a. Bats (usually) fly.
b. Animals which John fears (usually) fly.
Similarly, there is no logical necessity for the whale to be the largest
animal on earth, or for the quetzal to be Guatemala’s national bird; yet (10.a)
and (10.b) have the same respective truth conditions as (11.a) and (11.b):
(10) a. The whale suckles its young.
b. The quetzal has a magnificent, golden-green tail.
(11) a. The largest animal on earth suckles its young.
b. Guatemala’s national bird has a magnificent, golden-green tail.
Generics and frequency statements, then, are parametric on time, but
not on possible worlds; if two properties have the same extension throughout
time, they can be freely interchanged in a generic sentence salva veritate.
The third puzzle is how generics and frequency statement can be parametric
on one index but not on another.
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