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.
The symbolists attempted to purge poetry of all that was foreign to it, to concentrate upon essentials, and this meant the exclusion from art of those elements which in life had receded into the realm of the general, the commonplace. Thus the symbolists tended to repudiate outer actuality, which they identified with bourgeois civilization, and, retiring into themselves, to concentrate upon their own experience, which became more and more private and personal. The symbolists, if by that word we mean principally the poets Baudelaire, Verlaine and Mallarmé, were not led by their ideas to a repudiation of life, i.e., of experience. But in their search for an ideal Beauty lying behind the world of appearances their grip on actual life was weakened, and this made it easier for successors to turn away from actuality altogether and to preoccupy themselves with dreams. All art is rooted in experience. The flaw in symbolism, which helped to make possible its utilization by the exponents of aestheticism, was its imperfect realization of this truth and its too intense endeavour to break outside the limits of life, its over-specialization and the reactionary tendency which made it concentrate too exclusively upon the exotic, the bizarre. Symbolism and aestheticism must not, however, be confused. The first is a doctrine of art, springing from artistic practice; the second derives from theory and tends to become and attitude to life -- a very different thing. Yet it is not hard to see how this doctrine of art lent itself to the less austere and integral gospel of aestheticism which, as a way of apprehending life rather than a way of writing poetry, involved a turning away from actuality and a concentration upon certain elements in life which were considered to be superior to the rest.
As is well enough known, Yeats began his career in a literary environment heavily saturated with the aestheticism of Pater, of Wilde, and of the lesser figures of the eighteen-nineties, the dominant influences upon his mind being those of Pater and Villiers de L'Isle Adam, Axel being one of his "sacred books." Of the three main threads which ran together through his life and thought, each deriving from a common source: that is, aestheticism, natinoalism, and occultism, it is the first which may most profitably be taken as the key to his development. Yeats absorbed certain of the doctrines of Symbolism (as preached by Mallarmé) through the medium of Arthur Symons, who called him "the chief representative of that movement in our country." Nevertheless, Symbolism meant something quite different to the English followers than to their French masters. Baudelaire, Verlaine, and Mallarmé were not aesthetes; they were poets, seekers after reality, visionaries, and the practice of their art was rooted in, although it was an attempt to transcend, experience. It had a religious quality about it, and was in a sense the culmination of a mystical way of life, of apprehension. The aesthetes, however, who took over and adapted for their own uses the doctrines of Symbolism, lacked this intense seriousness. They were dilettantes, and interested less in the ardours of artistic creation than in the use to which artistic precepts could be put in the alleviation of living. The elements in life which aestheticism took to be superior to the others were its poetic elements, and therefore when they took to creative work their art was a reflection of a reflection. Dream and decoration were characteristics of their work because dream and decoration were what they sought for in life. Where the practice of poetry for Mallarmé implied a mystical vision of life, for Yeats it meant a turning away from life and the making of poetry out of moods and dreams, while his 'mysticism,' so far from being inherent in his artistic practice, was imported from outside in the form of the alien paraphernalia of theosophy, magic, and the rest.