§8. Within the last few years, however, a change has been taking place, a change due to several causes. In the first place, the literary criticism which was once taught exclusively in connection with classical authors and which claimed so large a part of the time allotted to classical study has found a more appropriate place in the departments of English that were hardly known a generation ago. In the second place, the superior preparation in the classics now demanded for admission to our colleges has relieved their courses of much elementary linguistic drill that was formerly necessary. In the third place, the last half century has seen a greater advance in the knowledge of Antiquities than all the years before, and it is now possible to present in positive dogmatic form much that was recently mere guesswork and speculation. Finally, modern theories of education, which have narrowed the stream of classical instruction only to deepen its channel and quicken its current, have caused more stress to be laid upon the points of contact between the ancient and the modern world. The teacher of the classics has come to realize that the obligations of the present to the past are not to be so clearly presented and so vividly appreciated in connection with the formal study of art and literature as in the investigation of the great social, political, and religious problems which throughout all the ages have engaged the thought of cultivated men. §9. Sources.--It has been already remarked (§6) that Classical Philology draws its knowledge from three sources, the literary, epigraphic, and monumental remains of Greece and Rome. It is necessary that we should understand at the outset precisely what is meant by each of these. By literary sources we mean the writings of the Greeks and Romans, that is, the books which they published, that have come down to us. The form of these books, the way they were published and have been preserved, will be considered later. For the present it is sufficient to say that a mere fraction only of these writings has come down to our day, and that of these poor remnants we possess no originals but merely more or less imperfect copies. It is true, nevertheless, that these form as a whole the most important of our sources of information, largely because they have been most carefully studied and are best understood.