Real life is, to most men, a long second-best, a perpetual compromise between the ideal and the possible; but the world of pure reason knows no compromise, no practical limitations, no barrier to the creative activity.
In the first place a philosophical proposition must be general. It must not deal specially with things on the surface of the earth, or within the solar system, or with any other portion of space and time. . . . This brings us to a second characteristic of philosophical propositions, namely that they must be a priori. A philosophical proposition must be such as can neither be proved nor disproved by empirical evidence. . . . Philosophy, if what has been said is correct, becomes indistinguishable from logic as that word has now come to be used.
Bertrand Russell (1872 - 1970)
Source: On Scientific Method in Philosophy, Russell