This lecture started from the question, what is a phenomenon, and how do we know of its existence? Seeing that our knowledge rests primarily on the evidence of our own mind, we drew the inference that Comte committed a fatal error when he banished the science of mind, as mind, from his cycle. Reviewing his various devices, and some devices of his successors, for eliminating psychology, and reducing the study of mind to a study of bodily functions, we approached the stronghold of Positivism,--law. And, after discussing the theories maintained respecting it, we boldly threw down our challenge to this effect: law phenomenal or mechanical admitted, we assert, the existence of another kind of law. We say that the freedom of human choice between evil and good is utterly unlike the freedom of a stone which falls by mechanical law, and cannot choose but fall. The inference from phenomenal law is the existence of a phenomenal world. The inference from another existent law is that there is another existent world. Man, we affirm, lives in both; has sympathies with both; and, by virtue of his double nature, is a true citizen of both. The ultimate principle of man's higher nature is to us inscrutable; for, even as the eye sees not itself, so neither does the spirit of a man discern that which makes it spirit. But, though we cannot know the soul, we can know much and many things about it; things most important--nay, all-important for us to know, since they distinguish the spirit that burns within us from matter, from mechanism, and from mere animality. Hence we do not, with the Positivist, ignore the unknowable. Contrariwise, confessing our ignorance, where we are ignorant, we strive to observe and gather all we can.