Strictly speaking, this is for the empiricist the limit of possible knowledge, but he would be a poor investigator who would be content with this and no more. The empiricist tries to go a distinct step in advance of this. The scientist observing the path of a planet travelling round the sun, finds that its course is that of an ellipse. He studies the path of a second planet, and finds that this also travels along an elliptical orbit. Later he finds that all planets he is able to observe travel in the same kind of path--then he hazards a general statement, and says, "All planets travel round their suns in elliptical orbits." But now he has left the realm of certainty for that of uncertainty. There may be innumerable planets which he cannot observe that take a different course. He hazards the general statement, because he assumes (sometimes without knowing that he does so) that nature is uniform and constant, that it will do to-day as it did yesterday, and does in infinite space as it does in the visible universe. The knowledge that is possible to the empiricist, then, is merely that which is derived from direct experience, and simple summations or generalisations into a single assertion of a number of similar assertions, all of which were individually derived from experience. This is the position scientists as such, and believers in the theory of naturalism, take up as to the possibility of the knowledge of truth to the human mind. They are entirely consistent, therefore, when they arrive ultimately at the agnostic position, and contend that our knowledge must necessarily be confined to the world of experience, and that nothing can be known of the world beyond. But they are fundamentally wrong in overestimating the place of the sense organs, and forgetting that while these have a part to play in life, they do not constitute the whole of life.