Such insight is extraordinary enough in the pre-Adamite epoch; but even more remarkable are his psychological foundations. The wealth of the State, he says, is the labor of its subjects, and they work because the wants of man are not a stated sum, but "multiply every moment upon him." The desire for wealth comes from the idea of pleasure; and in the _Treatise on Human Nature_ he discusses with superb clarity the way in which the idea of pleasure is related at once to individual satisfaction and to that sympathy for others which is one of the roots of social existence. He points out the need for happiness in work. "The mind," he writes, "acquires new vigor, enlarges its powers and faculties, and by an assiduity in honest industry both satisfies its own appetites and prevents growth of unnatural ones"; though, like his predecessor, Francis Hutcheson, he overemphasizes the delights opened by civilization to the humbler class of men. He gives large space in his discussion to the power of will; and, indeed, one of the main advantages he ascribed to government was the compulsion it puts upon us to allow the categories of time and space a part in our calculations. He does not, being in his own life entirely free from avarice, regard the appetite for riches as man's main motive to existence; though no one was more urgent in his insistence that "the avidity of acquiring goods and possessions for ourselves and our nearest friends is ... destructive of society" unless balanced by considerations of justice. And what he therein intended may be gathered from the liberal notions of equality he manifested. "Every person," he wrote in a famous passage, "if possible ought to enjoy the fruits of his labor in a full possession of all the necessaries, and many of the conveniences of life. No one can doubt but such an equality is most suitable to human nature, and diminishes much less the happiness of the rich than it adds to that of the poor." It is clear that we have moved far from the narrow confines of the old political arithmetic. The theory of utility enables Hume to see the scope of economics--the word itself he did not know--in a more generous perspective than at any previous time. It would be too much to say that his grasp of its psychological foundation enabled him entirely to move from the limitations of the older concept of a national prosperity expressed only in terms of bullion to the view of economics as a social science. But at least he saw that economics is rooted in the nature of men and therein he had the secret of its true understanding. _The Wealth of Nations_ would less easily have made its way had not the insight of Hume prepared the road for its reception.