ARISTOTLE's life is known to us in some detail from various sources, the chief being the Lives of the Philosophers by Diogenes of Laerte. He was born in 384 BC at Stageirus on the Gulf of the Strymon, and though he lived half his life at Athens he remained a citizen of that little colony in the North. His father was an hereditary member of the medical profession, and physician to King Amyntas II. of Macedon. At the age of seventeen Aristotle went for higher education to Athens. There this young son of a doctor from the colonies' became a pupil of Plato; and he was a member of the Academy for twenty years, till the founder's death. Plato called him the mind of the School.'Aristotle's debt to his master was very great; although in natural science he went far beyond him-his interest in biology he may have inherited from his father, in philosophy he built on Plato's foundations. He assumes in his readers a knowledge of Plato's writings; and if he only mentions him to differ from