Grice unlocks Hume's oyster with the aid of Locke

Hume writes in the “Appendix” that when he turns his reflection on himself, Hume never can perceive  this self without some one or  more perceptions. Nor can Hume ever perceive any thing  but the perceptions. It is the composition  of these, therefore, which forms the self, Hume thinks. Hume grants that one can conceive a thinking being to have either many or few perceptions. Suppose, says Hume, the mind to be reduced even below the life of an oyster. Suppose the oyster to have only one perception, as of thirst or hunger. Consider the oyster in that situation. Does the oyster conceive any thing but merely that perception? Has the oyster any notion of, to use Gallie’s pretentious Aristotelian jargon, self or substance? If not, the addition of this or other perception can  never give the oyster that notion. The annihilation, which this or that philosopher, including Grice’s first post-war tutee, A. G. N. Flew, supposes to  follow upon death, and which entirely destroys  the oyster’s self, is nothing but an extinction  of all particular perceptions; love and hatred,  pain and pleasure, thought and sensation. These therefore must be the same  with self; since the one cannot  survive the other. Is self the same with substance? If it be, how can that question have place,  concerning the subsistence of self, under  a change of substance? If they be distinct, what is the difference betwixt them? For his part, Hume claims, he has a notion of neither, when  conceived distinct from this or that particular perception. However extraordinary Hume’s conclusion may seem,   it need not surprise us. Most philosophers, such as Locke, seems inclined to think,  that ‘personal identity’ arises from  consciousness. But consciousness is nothing  but a reflected thought or perception,