The subject is aestheticism, the attitude toward art and literature at the end of the nineteenth century marked by "art for art's sake"; but, in showing how aestheticism differed from Symbolism, it is also one of the best presentations of Symbolism I have come by.
It is false to read this as qualifying Yeats's work. It is instead setting the groundwork to understanding Yeats's work.
From D.S. Savage's "The Aestheticism of W.B. Yeats," as presented in The Permanence of Yeats (ed. James Hall and Martin Steinmann, Macmillan, NY: 1950), a collection that should be on every Yeats scholar's shelf.
(Originally published in The Kenyon Review VII.1 (1945). Also published in Savage's The Personal Principle (George Routledge and Sons, London: 1944).)
If there are two key moments: The first is that symbolism derives not from theory (as does aestheticism) but out of literature and art itself. It is inherent to the practice of literature and art as Poetry. Indeed, it greatly defines that which is literature and art as Poetic. In turn there is the very important observation of the relationship of Poetry with reality and experience. The Symbolists were not then a school defined by an arbitrary practice, but were defined by their attempts to get at the hearth of the Poetic.
The second is how the fault of the Symbolists, getting separated from reality, was a fault of practice. At their worst they drifted too far into the symbolic and lost touch with experience, that element of art that makes it Poetry for the viewer as well as the maker. This is important because one of the critiques of the Symbolists, by extension one of the efforts to justify literature and art that is a-symbolic (the effort to ground Poetry in realism), lies in that drifting away from experience and into overly private systems of symbol. Recognizing that fault as a fault of practice and not of as inherent to symbolism per se eliminates the grounding of that critique.