The dictum ‘“ought” implies “can”’ has a status in moral philosophy in some respects like that of ‘a good player needs good co-ordination’ in talk about ball-games. Clearly, you say something important but not conclusive about proficiency in playing a ball-game when you say that it requires good co-ordination: similarly, you say something important but not conclusive about obligation when you say that it implies a certain possibility or power or ability. Each dictum is a reminder: the one about such courses of physical instruction, the other about such exhortations to duty, as are worth persevering with. It would be hopeless to keep on teaching a boy the moves and tricks of rugby football if he could never co-ordinate well enough to get his eye in, so to speak. Correspondingly, it would be meaningless to recommend that someone ought to do something the specification of which involved a contradiction, and pointless to suggest that he ought to do something which, for quite general reasons, was not, and was certain to remain not, within his power. So each dictum expresses a bluff, no-nonsense wisdom which we should count on before involving ourselves in certain more detailed commitments. But probably this is as far as the comparison between the two sayings can well be taken.

It will, I suppose, be readily agreed that questions concerning the scope of moral principles are of vital importance for the moral philosopher. If we are to accept a view, such as Professor Hare's, that there are formal criteria for any morality if it is to count as a morality, then it is necessary to know what is left outside the fence. Are Egoism and Caste Morality to count as moralities, restricted to the interests of one and of a limited group of persons respectively; or is there a logical absurdity in calling them moralities at all?

Hare's thesis of ‘prescriptive universalisability’, as definitive of the formal structure of any moral system, rules out such restricted ‘moralities’. Using ‘ought’ as a key-concept in moral discourse, Hare suggests that the word has two basic functions:

(i) to prescribe: meaning to commend courses of action sincerely to oneself and others.

(ii) to prescribe consistently, or universalisably; that is, in the same way, on relevantly similar occasions, to anyone, including oneself, unless valid reasons for discrimination of persons can be offered.

For a century or so after his death Hegel's system excited, if not wider diversity of interpretation and more bitter controversy, then certainly more bewilderment, than had ever before befogged the battlefields of speculative thought. A few fervent disciples maintained that their master had achieved a system substantially if not in all detail final and complete, a philosophy destined to set at rest forever all serious philosophic doubt. Others agreed that this claim to finality was inherent in the system, but mocked openly, proclaiming Hegel an arrogant megalomaniac.

‘When a dog runs, the dog is moving his legs; when a sea urchin runs, the legs are moving the sea urchin.’ Philosophers have come to appreciate the importance of understanding what action is. Their attempts at the clarification of ‘action’ have led them to talk of arms going up, muscles contracting, psychokinesis, bodies moving. They want to distinguish between sea urchins and dogs. Joined with the concept of action there is that of the person. Some are inclined to say we fail to understand action when we treat the agent as the responding organism; in such a view there is no room for ‘responsibility’, ‘duty’, ‘ought’, ‘intention’, ‘volition’. Man as responding organism cannot be distinguished from sea urchins or from complex mechanisms.

There is a story about a distinguished mathematician who had been invited to deliver a course of advanced lectures to other high-powered students of mathematics on a subject about which he was known to have some original ideas. The course, however, got off to a slow start. He devoted three lectures to discussing whether a certain proposition P was or was not self evident. The proposition P was essential to the argument he wanted to develop. Happily, he was able to announce at the opening of his fourth lecture that he had decided that P was self evident. There was an audible sigh of relief. It was now known, on the highest authority, that P was self evident. From that the argument proceeded briskly and with irresistible logic to the lecturer's surprising and devastating conclusions.