Euclid Of Megara, a Greek philosopher, born about 440 B. C. His first master was Parmenides; afterward he became a devoted disciple of Socrates, at whose death, according to Plato, he was present. But notwithstanding his affection for his second teacher, he retained from the Eleatic school an invincible tendency to subtlety, and it was said of him by Socrates that he knew how to live with sophists, but not with men. After the death of Socrates, his disciples, fearing for their lives, fled from Athens; and at Megara, in the house of Euclid, they found an asylum and a new centre for their studies. Plato himself was an ardent attendant upon Euclid, who taught that the essence of good was unity, unity so entire as to embrace immobility, identity, and permanence. Hence the sensible world has no moral character and no relation to good. He taught also that being consists only in unity, identity, and permanence, and hence the sensible world has no part in ex-istence. Being and good are thus the same thing, namely, unity; good therefore alone exists, and evil is but the absence of existence. It does not follow, however, that there is but a single being and a single sort of good, for unity may be found contained in various things.

Euclid expressly taught that in spite of their unity, being and good clothe themselves in different forms, present themselves under different points of view, and receive different names, as wisdom, God, intelligence, and others. Euclid also anticipated Aristotle in distinguishing the act from the power, and resolved according to his ideas of being the relation between the two.