It's not unusual to think of poetry as the speech-expression of pure pleasure principle (see John Latta's fine detective work today, re: Joan Retallack's playful writing).
But I can't help thinking of metaphysical or ontological implications. Though I know many poets & artists are opposed to metaphysics on principle. Anti-metaphysics can be a principled stance.
[An aside : but often it strikes me rather as a kind of complacent flatland of self-pleasing epicureans & blind egos (I'm not referring to either Latta or Retallack here, for heaven's sakes!). The self subsists always in relation to something or someone else...]
What I mean to say is that over the last few days I've been pondering along a parallel track to Retallack's comment, quoted at the end of Latta's post today. But maybe I'm thinking of it more abstractly or something. Poetry is distinct from other kinds of writing & language use in that it foregrounds & dramatizes (in & out of "performance") a living breathing speaker - even when there seems no rational reason to do so; in this way it (poetry) seems often to stumble over its own "feet", while ordinary language goes about its functional & impersonal business of declaring useful & necessary things.
& what exactly is happening here, in a linguistic sense? It seems to me that the pleasure of poetry pushes back against language's inherent alienation from that which it indicates. Poetry tries to close the ring of the space separating "horse" from actual horse. Paradoxically, it can only do this through a sort of playful embrace of solipsism and tautology. By focusing not so much on the real horse, but rather on its own imaginary song-horse, the poem, counter-intuitively, gives the horse itself a vivid sort of virtual reality. Thus poetry goes along singing its contrasting counter-melody, against all normal denotative indicative descriptive functional language-use.
The tendency in postmodern poetry has been to celebrate and revel in this contrast between poetic & ordinary speech. I think where I am leaning is toward the idea that all poetry - plain or obscure - whether the poets are conscious of it or not - all poetry is radically different from ordinary usage. This distinction gives evidence of poetry's link with archaic modes of intuition, prophecy and soothsaying, as well as ancient forms of praise & celebration.
It is possible, actually, to conceive of poetry's tautological ring-around-the-rosy as manifesting a form of knowledge-by-analogy, as in visual art - not by analysis or definition, but by modelling and implication...
(the end point being, perhaps, dramatic poetry : where theater & reality, play & history, come into intense engagement...)