Second problem: "PEgasus does not fly; so, something does not fly" (Grice, in Davidson/Hintikka, p. 119)

By J. L. Speranza
for the Grice Club.

After stating the eight 'natural inclinations', Grice notes two problems. The first would be that the represetation of a false existential statement (such as "Pegasus exists") would be a theorem. The second is perhaps trickier.

It starts, not with the law of identity, but with the unrestricted use of UI and EG as stated in the sixth natural inclination.

We start with step 1

1. ~Fa.

We reach a second step by Existential generalisation:

2. (Ex)~Fx

In the light of the third natural inclination, Grice notes, 'this seeminlgy licenses' the following:

Pegasus does not fly
________________________
-.
. . Something does not fly.


"But," Grice notes, "such an inference seems illegitimate". And it seems illegitimate, if, in the light of the fifth natural inclination, 'It is not the case that Pegasus flies' is TRUE on the strengh of Pegasus not existing -- as the second natural inclination allows.

Grice notes: "One SHOULD not be able, it seems,

to assert that something does NOT fly on the

basis of the truth of a statement to the effect that

a certain admittedly non-existent object does not fly."

Unless you are Mary Poppins.