Henry George,
Progress and Poverty, Volumes I and II
“ The fundamental principle of human action—the law that is to political economy what the law of gravitation is to physics—is that men seek to gratify their desires with the least exertion. Evidently, this principle must bring to an equality, through the competition it induces, the reward gained by equal exertions under similar circumstances. When men work for themselves, this equalization will be largely affected by the equation of prices; and between those who work for themselves and those who work for others, the same tendency to equalization will operate. ”
