Thus the senses, although feeble and erring guides, are, after all, the gates to knowledge; and their reports, when tested by the light of reason, form the data for human speculation. The senses, resident in the limbs, are composed in certain proportions of the four elements, which also constitute the earth. Therefore, between the frame of man and the world outside him, there is a community of substance, whereby he is enabled to know. #Homoia homoiois gignôsketai# (likes are known by likes) is the foundation of our philosopher's theory of knowledge. The rational soul, being that immortal part of man whereon depends his personal identity, whether he take the shape of plant or animal, receives and judges the results of sensation. This theory, it will be observed, has a kind of general similarity to that of Parmenides. Empedocles draws a marked difference between the province of the senses and of the reason, and inveighs against the impotence of the former. Again, he speaks of the real being of the world as pure and perfect intellect; and at the same time elaborately describes the universe as it appears to human sense and understanding. But here the likeness ends. Parmenides has no mysticism, and indulges in no theology. He believes in the actual truth of his rational ontology, and sneers at the senses. "Thy fate it is," he says, "all mysteries to learn, both the unswerving mind of truth that wins a sure assent, and the vain thoughts of men, in which no certainty abides. But, baseless as they are, these also shalt thou learn; since thou must traverse every field of knowledge, and discern the fabric of the dreams of men." His ontology is just as elaborate as his physics, and he evidently considers its barren propositions of more value than any observations on astronomy or physiology. Empedocles, on the other hand, despaired of ontology, and gave all his mind to explanations of the physical universe--how it came to be, and what laws governed its alternations--believing all along that there was a higher region of pure intellect beyond the reach of his degraded soul. "Here we see in a glass darkly, but then face to face." In this respect he resembled Xenophanes more than Parmenides. Xenophanes had said, "No man hath been, nor will ever be, who knows for certain all about the gods, and everything of which I speak; for should one publish the most sure and settled truth, yet even he cannot be said to _know_: opinion is supreme in all things." Empedocles belonged more to the age behind him than to that which followed; and his extensive knowledge of nature was a part of his artistic rather than his scientific temperament.