T HE interpretation of Plato's philosophy presented in the following pages accepts the position that each of Plato's dialogues may be used as evidence of his own thought at the time he wrote it. He clearly did not accept all the doctrines which he put in the mouths of his principal speakers; yet these doctrines indicate the chief subjects of his philosophical speculation, without confining his thought to a rigid system. I use the chronology of the dialogues as it is now almost universally accepted, and on the basis of this chronology I differentiate between an earlier and a later Platonism. It is not possible to demonstrate the validity of this position; it is justified only in so far as it makes possible a coherent formulation of Plato's philosophy. Causation may be described as a relatioxi of which one term produces or determines the existence or character of the other term. The concept of a cause was first formulated not long before the time of Plato. In the earliest Greek literature the word a'lrLos is used in reference to responsibility, usually with the added connotation of blame.' The extension of the notion of responsibility to all the objects and events of experience marks the beginning of the study of causation. The early Greek philosophers, so far as we know, did not speak specifically of causes; yet their systems may be considered as