So again, even those who hold that moral rules are only obligatory because it is the individual’s interest to conform to them--thus regarding them as a particular species of prudential rules--do not thereby get rid of the ‘dictate of reason,’ so far as they recognise private interest or happiness as an end at which it is ultimately reasonable to aim. The conflict of Practical Reason with irrational desire remains an indubitable fact of our conscious experience, even if practical reason is interpreted to mean merely self-regarding Prudence. It is, indeed, maintained by Kant and others that it cannot properly be said to be a man’s duty to promote his own happiness; since “what every one inevitably wills cannot be brought under the notion of duty.” But even granting[38] it to be in some sense true that a man’s volition is always directed to the attainment of his own happiness, it does not follow that a man always does what he believes will be conducive to his own _greatest_ happiness. As Butler urges, it is a matter of common experience that men indulge appetite or passion even when, in their own view, the indulgence is as clearly opposed to what they conceive to be their interest as it is to what they conceive to be their duty. Thus the notion ‘ought’--as expressing the relation of rational judgment to non-rational impulses--will find a place in the practical rules of any egoistic system, no less than in the rules of ordinary morality, understood as prescribing duty without reference to the agent’s interest.