The more strict defence of poetry was attempted for the most part on the grounds set forth by Horace in his _Ars Poetica_. At no period from the Augustan Age to the Renaissance does the _Ars Poetica_ seem to have been entirely lost. It is mentioned or quoted, for example, by Isidore of Seville[13] in the sixth century, by John of Salisbury[14] in the twelfth century, and by Dante[15] in the fourteenth. Horace insists on the mingled instructiveness and pleasurableness of poetry; and beyond this, he points out the value of poetry as a civilizing factor in history, regarding the early poets as sages and prophets, and the inventors of arts and sciences:-- "Orpheus, inspired by more than human power, Did not, as poets feigned, tame savage beasts, But men as lawless and as wild as they, And first dissuaded them from rage and blood. Thus when Amphion built the Theban wall, They feigned the stones obeyed his magic lute; Poets, the first instructors of mankind, Brought all things to their proper native use; Some they appropriated to the gods, And some to public, some to private ends: Promiscuous love by marriage was restrained, Cities were built, and useful laws were made; So ancient is the pedigree of verse, And so divine the poet's function."[16] This conception of the early poet's function was an old one. It is to be found in Aristophanes;[17] it runs through Renaissance criticism; and even in this very century, Shelley[18] speaks of poets as "the authors of language, and of music, of the dance, and architecture, and statuary, and painting," as "the institutors of laws, and the founders of civil society, and the inventors of the arts of life." To-day the idealist takes refuge in the same faith: "The tree of knowledge is of equal date with the tree of life; nor were even the tamer of horses, the worker in metals, or the sower, elder than those twin guardians of the soul,--the poet and the priest. Conscience and imagination were the pioneers who made earth habitable for the human spirit."[19]