=The Difficulties in Understanding the Teaching of Plato.= The theory of Plato is one of the most involved and one of the most difficult to understand in the whole history of philosophy. This difficulty of interpreting Plato as a philosopher depends upon many factors: upon the artistic literary form of the dialogue in which his philosophy is presented; upon the conflicting tendencies of thought in Plato himself; upon the fact that the composition of his dialogues extended over a period of more than half a century; upon the constant reshaping of the content as well as the form of his thought; and upon the uncertainty of the chronological order of his writings. This chronological order of Plato’s dialogues is an important factor in determining his teaching. Since the beginning of the nineteenth century a vast amount of literature has been published on the subject, and many theories of the dialogue-chronology have been proposed. There are three principal groups of theories: (1) those based upon purely _a priori_ hypotheses, as, for example, that of Hermann, that each dialogue is a stage in the development of Plato’s thought; or that of Schleiermacher, that Plato had a systematic plan from the beginning; (2) those based upon an empirical study of the historical allusions in the dialogues themselves (Zeller, Windelband, _et als._); (3) those recent theories based upon the “stylometric test,” _i. e._ by an examination of the peculiarities of the style of Plato. Lutoslawski is a prominent representative of this method. The result to the student is bewildering, on account of the differing conclusions. But since some choice must be made, we shall follow the order laid down by Windelband,[26] because it is fairly orthodox and conservative. For convenience to the memory, the writings will be grouped in the periods of Plato’s life. Our interpretation will therefore follow Windelband in respect to the character of Plato’s theory itself. =The Life and Writings of Plato.= Two important events divide Plato’s long life of eighty years into three periods. These events were the death of his master, Socrates, in 399 B. C., and Plato’s return from Sicily in 387 B. C., after having there come under the influence of the Pythagoreans. His first period may be called his student life, and was twenty-eight years long; the second period was that of the traveler, and was twelve years long; the third period was that of teacher of the Academy, and was forty years long. The first half of his life therefore covers the first two periods, and the second half covers his period as teacher. Probably he was engaged in the composition of the dialogues during all these periods, and Cicero reports him to have died “pen in hand” (_scribens est mortuus_). =1. Plato’s Student Life= (427–399 B. C.). This period closes with the death of Socrates. His acquaintance with Socrates began when he was twenty years old, and therefore lasted eight years.