Being original and innate, it measures the responsiveness of the individual to this or that motive, and those alone, to which he is specially sensitive, will appeal to him with anything like compelling force. As in chemistry, with unchangeable certainty, one substance reacts only upon acids, another only upon alkalies, so, with equal invariableness, different natures respond to different stimuli. The motives suggesting loving-kindness, which stir so deeply a good disposition, can, of themselves, effect nothing in a heart that listens only to the promptings of Egoism. If it be wished to induce the egoist to act with beneficence and humanity, this can be done but in one way: he must be made to believe that the assuaging of others' suffering will, somehow or other, surely turn out to his own advantage.

What, indeed, are most