Having at length, after twenty years devoted to the training of the
 young, obtained leisure for study, I was asked by certain of my friends
 to write something on the art of speaking. For a long time I resisted
 their entreaties, since I was well aware that some of the most
 distinguished Greek and Roman writers had bequeathed to posterity a
 number of works dealing with this subject, to the composition of which
 they had devoted the utmost care. This seemed to me to be an admirable excuse for my refusal, but served
 merely to increase their enthusiasm. They urged that previous writers on
 the subject had expressed different and at times contradictory opinions,
 between which it was very difficult to choose. They thought therefore
 that they were justified in imposing on me the task, if not of
 discovering original views, at least of passing definite judgment on
 those expressed by my predecessors. I was moved to comply not so much because I felt confidence that I was
 equal to the task, as because I had a certain
 compunction about refusing. The subject proved more extensive than I had
 first imagined; but finally I volunteered to shoulder a task which was
 on a far larger scale than that which I was originally asked to
 undertake. I wished on the one hand to oblige my very good friends
 beyond their requests, and on the other to avoid the beaten track and
 the necessity of treading where others had gone before.