The answers that we may give to these questions together constitute a philosophy of evolution, which is carefully to be distinguished from evolution as a scientific theory. As a scientific theory evolution is an account, as exact as science can make it, of what actually did happen in the past, of the precise process by which things have come to be what they are. When this knowledge has been gained, we may ask the question, What value has this knowledge for the practical purposes of life? And the answer will be a contribution to philosophy, but it will not be one of the things described by science as having happened in the past, will not be part of the knowledge from which it is itself inferred, nor, if it is a false inference, will it have any right to masquerade as science and say that we must accept it as true or else deny the truth of science. Indeed, we found that two answers to the question, two philosophies of evolution, the Optimistic and the Pessimistic, have been formulated, which being contradictory cannot both be true, though both may be false. The Optimistic theory, that evolution is progress, only established its conclusion, that the process of evolution is necessarily from good to better, by means of arguments which denied the distinction between good and bad, and implied that our moral convictions were illusions. The Pessimistic theory, on the other hand, assumed the reality of our moral ideals, but was forced by its adoption of the theory of Necessity to conclude that it is an illusion to imagine those ideals can be finally realised. Both philosophies in theory profess to make no assumptions, to take nothing on faith, and to base themselves on nothing but what we actually know to be facts. In practice each of them does unconsciously base itself on faith and does tacitly make certain assumptions. But as the assumptions made are not precisely the same in both cases, they reach two very different conclusions--Optimism and Pessimism. Again, if each philosophy treats as illusions certain facts--the freedom of the will and the reality of moral distinctions--which the common sense and common consciousness of mankind hold to be real, it is because each philosophy arbitrarily rejects certain of the assumptions which common sense makes, certain articles of the common faith of mankind. Consequently, when we find that each philosophy is inconsistent with itself, and ends by implying that what it assumed to be real is in fact an illusion, we are led to suspect that its assumptions may not have been adequate or well-considered, its faith not great enough to remove mountains or explain the world.