Discussions on poetry:
The Making of a Poem, by Stephen Spender
The Romantic Imagination, by C. M. Bowra
Archetypal Patterns in Poetry: Psychological Studies of Imagination, by Maud Bodkin
The Fortunes of Epic Poetry: A Study in English and American Criticism 1750-1950, by Donald M. Foerster
Chaucer: Poet of Mirth and Morality, by Helen Storm Corsa
Symbol and Myth In Ancient Poetry, by Herbert Musurillo
Look for these books in the literary criticism.
