A first principle seems to depend on what Andy Clark pointed out, that the mind has a deliberative verbal processor and an associative intuitive processor which have utterly different properties. So the mind is a hybrid; we have to negotiate between the different modes. The verbal processor can enable thoughts themselves to be objects of thought. The associative processor is perhaps responsible for concepts and intuitions. A verbal utterance, received by the verbal processor can be purely semantic and syntactic. I can write: "There's a leafless tree outside my window." In these words I can communicate both to myself and you. Perhaps you can think of a tree of this kind. This isn't poetic: you know the sort of thing I mean by drawing on your experience of winter-time deciduous trees. A poetic utterance does this but adds something beyond the semantic and syntactic. It makes connections between and among the words themselves by means such as metres, metaphors, metonyms, multiple interpretations. The psychological effect of an evocative poem is to invite a certain density of reflective thought, which brings a thought feelingfully to mental presence, by its several links with the associative processor. (On this idea of reflectiveness, see Sikora, Miall & Kuiken click here.) If I read, in William Shakespeare's Sonnet 73 the line: "Bare ruined choirs, where late the sweet birds sang," the words seem to become poetic by inviting links from the verbal to the intuitive processor that go beyond the semantic and syntactic because they are multiple and simultaneous. Rather than intuitions one-at-a-time, they invite concurrent intuitions. In this line, I enjoy the iambic pentameter because it's like a heartbeat; I think somewhat poignantly of my own aging as of ruined churches I have visited along the English-Scottish border, picturesque but sad, no longer of much use except as memories of a sort; I connect the singing of birds and the singing of choirs; I wonder what birds were doing, flying about in the churches before they were ruined. All in ten syllables: the span of a single conscious verbal thought. If I had merely written such thoughts (as I have just done), you'd read them one at a time, they'd not be linked, and they'd not be of much interest.
A second principle, as John Keats said in a letter of 27 February 1818, is that: "Poetry should surprise by a fine excess and not by Singularity." (In North American usage: it should be unusual but not weird.) The principle was later proposed by Victor Shklovsky: defamiliarization. It was one of the first aspects of literature to be studied empirically, by Willie van Peer. Rachel Giora has shown that brain activation spreads beyond the language hemisphere not in response to metaphoricity, but to unusualness.
A third principle derives from Indic poetics, in which Abhinavagupta said that dhvani, suggestiveness, is the heart of poetry. Suggestiveness implies an intimate partnership: the poet suggests and the hearer or reader creates a shared meaning.
And, as Coleridge said, real "poetry brings the whole soul … into activity." How it does so is what we're trying to understand: trying, but not there yet.
Clark, A. (2006). Material symbols. Philosophical Psychology, 19, 291-307.
Coleridge, S. T. (1817). Biographia literaria, Ed J. Shawcross. Oxford: Oxford University Press (current edition 1907).
Giora, R. (2007). Is metaphor special? Brain and Language, 100, 111-114.
Ingalls, D. H. H., Masson, J. M., & Patwardhan, M. V. (1990). The Dhvanyaloka of Anandavardana with the Locana of Abhinavagupta. Cambridge, MA.: Harvard University Press.
Keats, J. (1816-20). Selected poems and letters of Keats (Ed. D. Bush). New York: Houghton Mifflin (current edition 1959).
Shklovsky, V. (1919). On the connection between devices of Syuzhet construction and general stylistic devices. In S. Bann & J. E. Bowlt (Eds.), Russian formalism: A collection of articles and texts in translation (pp. 48-71). Edinburgh: Scottish Academic Press (this edition 1973).
Sikora, S., Kuiken, D., & Miall, D. S. (2011). Expressive reading: A phenomenological study of readers’ experience of Coleridge’s “Rime of the Ancient Mariner.” Journal of Aesthetics, Creativity, and the Arts 5, 258-268.
Van Peer, W. (1986). Sylistics and psychology: Investigations of foregrounding. London: Croom Helm.
Vendler, H. (1997). The art of Shakespeare's sonnets. Cambridge, MA: Harvard University Press.