The question why we are ‘bound’ by moral requirements is as old as it is fundamental. Its interest is both practical and theoretical. Its practical interest comes out in this way: nothing is easier—at least on occasion—than to disregard the restraints imposed by morality. In submitting to them we must often forgo what we would otherwise desire. A man may have sacrificed much in the interests of ‘behaving well’. He may wish therefore to know whether his sacrifice has been foolish. It is only reasonable to ask why we are ‘bound’, if indeed we are. Scepticism on this point is not merely playful. We want to know the reason (at least in outline) for accepting moral restraints. I say ‘at least in outline’ because just as it may be reasonable to act on your doctor's advice although you do not understand his reasons in detail, so it may be reasonable to accept advice on some moral matter although you do not understand its justification in detail.