In his struggle against Hume, Kant was not concerned to challenge his opponent's definition of man's reasoning power. His sole object was to show that, if one accepted this definition, one must not go as far as Hume in the application of this power. All that Kant could aspire to do was to protect the ethical from attack by the intellectual part of man, and to do this by proving that the former belongs to a world into which the latter has no access. For with his will man belongs to a world of purposeful doing, whereas the reason, as our quotations have shown, is incapable even in observing external nature, of comprehending the wholes within nature which determine natural ends. Still less can it do this in regard to man, a being who in his actions is integrated into higher purposes.