The kind of sceptical difficulty he considers arises naturally from the argument he has developed.
Moral scepticism is the specific problem which haunts moral epistemology.
The sceptic can deny that there is any moral knowledge or justified moral belief. This amoralistic scepticism implies non-cognitivism in morality and a radical form of externalism regarding moral motivation. Moral knowledge or justified belief is simply practically inert. This type of moral scepticism is a variation on a difficulty in the philosophy of mind usually referred to as the problem of other minds. How is it possible to know the mind, eg.