Materialism, like any system of natural philosophy, carries with it no commandments and no advice. It merely describes the world, including the aspirations and consciences of mortals, and refers all to a material ground. The materialist, being a man, will not fail to have preferences, and even a conscience, of his own; but his precepts and policy will express, not the logical implications of his science, but his human instincts, as inheritance and experience may have shaped them. Any system of ethics might accordingly coexist with materialism; for if materialism declares certain things (like immortality) to be impossible, it cannot declare them to be undesirable. Nevertheless, it is not likely that a man so constituted as to embrace materialism will be so constituted as to pursue things which he considers unattainable. There is therefore a psychological, though no logical, bond between materialism and a homely morality. The materialist is primarily an observer; and he will probably be such in ethics also; that is, he will have no ethics, except the emotion produced upon him by the march of the world. If he is an _esprit fort_ and really disinterested, he will love life; as we all love perfect vitality, or what strikes us as such, in gulls and porpoises. This, I think, is the ethical sentiment psychologically consonant with a vigorous materialism: sympathy with the movement of things, interest in the rising wave, delight at the foam it bursts into, before it sinks again. Nature does not distinguish the better from the worse, but the lover of nature does. He calls better what, being analogous to his own life, enhances his vitality and probably possesses some vitality of its own. This is the ethical feeling of Spinoza, the greatest of modern naturalists in philosophy; and we shall see how Lucretius, in spite of his fidelity to the ascetic Epicurus, is carried by his poetic ecstasy in the same direction.