This social condition, to which the protective theory would logically lead, is the lowest in which man is ever found – the condition from which he has toiled upward. He has progressed only as he has learned to satisfy his wants by exchanging with his fellows and has freed and extended trade. The difference between naked savages possessed only of the rudiments of the arts, cowering in ignorance and weakness before the forces of nature, and the wealth, the knowledge and the power of our highest civilization, is due to the exchange of the independence which is the aim of the protective system, for that interdependence which comes with trade. Men cannot apply themselves to the production of but one of the many things human wants demand unless they can exchange their products for the products of others. And thus it is only as the growth of trade permits the division of labor that, beyond the merest rudiments, skill can be developed, knowledge acquired and invention made; and that productive power can so gain upon the requirements for maintaining life that leisure becomes possible and capital can be accumulated.