Now I designate Beauty as the province of the poem, merely because it
is an obvious rule of Art that effects should be made to spring from
direct causes—that objects should be attained through means best
adapted for their attainment—no one as yet having been weak enough to
deny that the peculiar elevation alluded to is most readily attained
in the poem. Now the object Truth, or the satisfaction of the
intellect, and the object Passion, or the excitement of the heart,
are, although attainable to a certain extent in poetry, far more
readily attainable in prose. Truth, in fact, demands a precision, and
Passion, a homeliness (the truly passionate will comprehend me), which
are absolutely antagonistic to that Beauty which, I maintain, is the
excitement or pleasurable elevation of the soul. It by no means
follows, from anything here said, that passion, or even truth, may not
be introduced, and even profitably introduced, into a poem for they
may serve in elucidation, or aid the general effect, as do discords in
music, by contrast—but the true artist will always contrive, first, to
tone them into proper subservience to the predominant aim, and,
secondly, to enveil them, as far as possible, in that Beauty which is
the atmosphere and the essence of the poem. -- Edgar A. Poe, The
Philosophy of Composition
Ditto for songs.