Grice defines 'belief' in terms of 'desire'

Grice was well aware that behaviourism in wrong. We need 'belief' or 'desire' as THEORETICAL concepts. It doesn't matter much, he thought, which one we use as primitive. He opted for 'desire'.

Thus, 'belief' gets defined as follows:

--- from "Conception of Value":


"X believes that p iff X desires as follows: given any situation in which

1. X wills some end E

2.There are two non-empty classes K1 and K2 of action types such that the performance by X of an action type belogning to K1 will realise E just in case p IS TRUE, and the performance by X of a member of K2 will realise E just in case p is false.

3. There is no third non-empty class K3 of action types such that the performance by x of an action type belonging to K3 will realise E whether p is true or p is
false,

THEN, in such situation, x is to will that he perform some
action-type belonging to K1.

Gr91:152.

Ah! if philosophers of mind were ever so careful as this philosophical psychologist!