Largo espectro de plata conmovida
el viento de la noche suspirando,
abrió con mano gris mi vieja herida
y se alejó: yo estaba deseando.
Llaga de amor que me dará la vida
perpetua sangre y pura luz brotando.
Grieta en que Filomela enmudecida
tendrá bosque, dolor y nido blando.
A lot of the words seem very ordinary (noche, luz, mano) but the constant placement of the adjectives before the nouns and the gives the passage a literary feel (largo espectro, vieja herida, perpetua sangre, pura luz). Not to mention the mythological allusion and the Petrarchan language (llaga de amor).
Then learning to read and interpret this kind of poetry is simply a matter of knowing the metaphorical codes and being accustomed to the elevation in style. Love is a wound (herida, llaga). A long phantom of impassioned silver sighing the wind of the night opened with grey hand my old wound... etc... Filomela, the nightingale, represents poetry.
It might seem simple to do away with elevated language and write poetry in a language that is really spoken. The Wordsworthian ideal. But in practice this is not so easy to do. Poetic language wants to be different from ordinary, and it will find a way to get there.
As I sd to my(Creeley)
friend, because I am
always talking, John, I
sd, which is not his
No elevation of style, no conventional Petrarchianism, but it is not easier poetry to interpret. In fact, the absence of literary code makes it almost impenetrable. If you try to find a literary code that isn't there you will end up with one of those highschoolish Christian readings of the poem that I've heard about. Colloquialism also seems to be a deliberately anti-literary gesture, so elevation of style persists in its very absence.
There are also styles that seem colloquial but are really not, like Creativewritingese: "I stare at the sky / for days." Nobody talks about actions in the present tense like that unless they are writing a pome. The words might be perfectly ordinary, but the gesture is literary. A truly colloquial or prosaic style (two different things, by the way) is often hard to accept in a poem.
Prosiness still often sounds like its making a prosy gesture, away from literary elevation and poetic concision. Otherwise, what is it doing? If it looks like its being used unconsciously, then the reader might think it's simple incompetence. Colloquialism is easier to accept than prosiness, because it come from the spoken rather than the written language, but colloquialism can mean several things: a plain vanilla neutrality, a deliberately "low" register, or an actual imitation of real life speech patterns. But whose?
So once you get rid of the simplistic idea that poetic language distinguishes itself by being more elevated and literary in the conventional sense, you get a complex and bewildering situation that nobody quite understands. I certainly don't. There may be an unarticulated ideal of a language elegant but not too elevated, colloquial but not too colloquial, distinguishable not by its diction or rhetoric or metaphorical codes but by its purity of gesture. I find this ideal in certain poems by Machado, for example.