in either case the method is the same. This profession may be most
 briefly considered under two heads, the art of speaking correctly and
 the interpretation of the poets; but there is more beneath the surface
 than meets the eye. For the art of writing is combined with that of speaking, and correct
 reading precedes interpretation, while in each of these cases criticism
 has its work to perform. The old school of teachers indeed carried their
 criticism so far that they were not content with obelising lines or
 rejecting books whose titles they regarded as spurious, as though they
 were expelling a supposititious child from the family circle, but also
 drew up a canon of authors, from which some were omitted altogether.
 Nor is it sufficient to have read the poets only; every kind of writer
 must be carefully studied, not merely for the subject matter, but for
 the vocabulary; for words often acquire authority from their use by a
 particular author. Nor can such training be regarded as complete if it
 stop short of music, for the teacher of literature has to speak of metre
 and rhythm: nor again if he be ignorant of astronomy, can he understand
 the poets; for they, to mention no further points, frequently give their
 indications of time by reference to the rising and setting of the stars.
 Ignorance of philosophy is an equal drawback, since there are numerous
 passages in almost every poem based on the most intricate questions of
 natural philosophy, while among the Greeks we have Empedocles and among
 our own poets Varro and Lucretius, all of whom have
 expounded their philosophies in verse.