It may seem, he admits, that ``since interest, one's own happiness, is a manifest obligation'', in any case in which virtuous action appears to be not conducive to the agent's interest, he would be ``under two contrary obligations, i.e. under none at all. But'', he urges, ``the obligation on the side of interest really does not remain. For the natural authority of the principle of reflection or conscience is an obligation … the most certain and known: whereas the contrary obligation can at the utmost appear no more than probable: since no man can be certain in any circumstances that vice is his interest in the present world, much less can he be certain against another: and thus the certain obligation would entirely supersede and destroy the uncertain one.''---(Preface to Butler's Sermons.)