In the seventh _Epistle_ of the first book Horace refuses, at least for the present, an invitation of Mæcenas, on the ground that his health is poor and that he needs the repose of the country and the seashore. At the same time he explains the manner in which he wishes his relation to his patron to be understood. He is not a parasite, and openly says that he must retain his freedom, and can not be at the beck and call even of Mæcenas. In the first _Epistle_ (lines 4 and 10) he refuses to write more odes, because he is no longer young and is turning toward philosophy. [Sidenote: The second book of Epistles.] The same attitude is disclosed in the second _Epistle_ of the second book (lines 25 and 141 ff.). The poet wished to retire and pursue the study of philosophy; but he had gained much experience in literary matters, and in three letters, written probably between 19 and 14 B. C., he records the results of this experience. The first letter is addressed to Augustus, the second to Julius Florus. These two form the second book of the _Epistles_. The third letter, addressed to the Pisos, father and two sons, was originally published with the others, but was [Sidenote: The Ars Poetica.] soon separated from them, and is known as the _Ars Poetica_. This is not a systematic treatise on poetry, but Horace’s views, derived in part from his own experience, in part from his reading, are set forth in the easy style of a letter or talk. He insists that each poem must have a consistent fundamental idea or plot, that the characters of a drama must speak as befits their age and station, and must be drawn from life, he advises care in the choice of a subject, points out that nobody cares for mediocre poets, and that what is once published can not be recalled. Throughout the letter or treatise he constantly impresses upon his readers his conviction that good poetry is the result of hard work. Many critical and historical remarks are scattered through the _Ars Poetica_ as well as through the two other letters.