This introduction presents an overview of key concepts discussed in the subsequent chapters of this book. The book discusses the Essence of Plato's Philosophy. Plato was a descendant of one of the foremost families of the ancient Attic aristocracy. People are better able to pass judgment on Plato as philosopher than they are on all other Greek philosophers. Much effort has been spent in distinguishing between the purely Socratic and purely Platonic thought in the dialogues of Plato's youth; therefore careful attention has been given to the expressions which deal with the relation of the concepts to the particular things. From of old the philosophy of Plato has been looked upon as having the characteristic of taking the concepts and hypostatizing them or making substances. The faith in the absolute dependability of Aristotle's interpretation was severely shaken. In this manner he misinterprets the Pythagoreans several times and also grossly misunderstands several passages in the Republic and the Laws.