Many years ago when I was in college, a professor of mine was struggling to define poetry; that is, to identify those characteristics that all good poems have in common. After several unsuccessful attempts at a definition, she finally declared, in frustration, that poetry is where the writer tells the editor how to arrange the words on the page.
Now, while there is some truth to this characterization, it struck me then, and still does now, that it is more glib than enlightening. And so I have been thinking lately about what characterizes good poetry; that is, what are the bare essentials of a good poem.
(I specify 'good poetry' because there are few things that annoy me more than bad poetry. Bad poetry cannot be excused. It is possible to excuse bad singing, or bad dancing or bad drawing because all of us do these things more or less poorly. But few people attempt poetry, and when they do so unsuccessfully, it is embarrassing.)
I would say that there are three, or perhaps four, characteristics of all good poetry. These are, to begin with, Intensity, Imagery, and Rhythm. Poetic language must be intense, that is, it must convey a great deal of meaning in very few words; the more meaning and the fewer words the better. Poetry is the most intensive form of language, and the very best poetry challenges our ability to grasp all at once the meaning of the poet. When G. M. Hopkins says in talking about the relation of body to soul, 'Self-yeast of spirit a dull dough sours' or 'As tumbled over rim in roundy wells stones ring' he is packing the phrases with a density of meaning and a beauty of expression that would be impossible in prose.
Above all, poetry is metaphoric in nature. Poetic language must invoke images or sensory perceptions in the mind of the reader. More so than any other form of literature, poetry moves on a suspension bridge-work of metaphor in conveying meaning from the mind and soul of the poet to those of the reader. And the more unusual, unexpected, yet telling the imagery, the more effective the poetry. When e.e. cummings says of his beloved, 'No one, not even the rain, has such small hands,' he is being at once tender and vividly unexpected in his choice of words and image. Hands and raindrops have nothing in common, are never taken together, yet in overlapping them as he does, he creates an impression that is at once original, clear, and moving. And John Donne (one of the greatest poets in English) gives us perhaps the most unusual yet precise and lovely image for two lovers when he compares them to 'the stiff twin compasses' which engineers and geometers use to draw circles. 'Thy soul, the fixed foot, makes no show to move, but doth if th'other do.' The lovers are joined at the pinnacle of their beings, yet they move, seemingly independently of one another. But the separation is only seeming: the foot of the compass that runs and describes the circle is held firm by the fixed foot, which 'leans and harkens after it', keeping its 'circle just' and inevitably drawing it home.
Thirdly, poetry is characterized by the deliberate use of rhythm. Poetic language is always rhythmical, because poetry is the closest of all the linguistic arts to music, which is the greatest of all the arts. Whether formal and rigid, as in the Elizabethan sonnet, or loose and suggested as in some twentieth century poetry, rhythm is always a component of good verse, giving its language cohesion, momentum and intrinsic structure and beauty. In Anthem for Doomed Youth, Wilfred Owen tells us that the true eulogy for the slaughtered boys of World War I lies not in official declamations but, 'Their flowers the tenderness of patient minds/ And each slow dusk, a drawing-down of blinds.' This careful and solemn use of rhythm is itself a suitable funeral dirge for the dead.
A fourth characteristic of poetry, which is neither inevitable nor even necessary, is rhyme. Yet rhyme is the first thing that comes to mind when most people are asked what makes poetry poetic. But modern verse has made it clear that rhyme is dispensable, and many poets and many poems do without it altogether. (Though as a practical mater, the loss of rhyme must be accounted for by a careful attention to rhythm. Rhythm, when well executed, can take the place of rhyme as an effect in verse.)
Nonetheless, rhyme was a constant in early poetry, and remains a popular device in the making of a poem. Shakespeare even found it useful to use rhyme in the course of the prose in his plays, either to denote the end of a speech or scene, or to create a ringing effect, as when Hamlet says, 'The play's the thing in which I'll catch the conscience of the king.' Or when Cladius, at the end of his prayer, laments, 'My words fly up, my thoughts remain below/ Words without thoughts never to heaven go.'
I suggest that Shakespeare knew full well that by rhyming, he would leave the audience with the strong impression of a pithy and quotable phrase, as indeed, he did. And even T.S. Eliot, for whom rhyme was far from indispensable, felt compelled to use it in order to nail down, as it were, certain salient ideas. At the end of The Love Song of J. Alfred Prufrock, for example, in a wonderful example of imagery, rhythm and rhyme, he has Prufrock say of the mermaids, 'I have seen them riding seaward on the waves/ Combing the white hair of the waves blown back/ When the wind blows the water white and black./ We have lingered in the chambers of the sea/ By sea girls wreathed with seaweed red and brown/ Til human voices wake us, and we drown.'
Beyond these three or four qualities, I can think of no constants in good poetry, except perhaps for that of meaning. A poem that does not convey a clear and profound meaning from poet to reader is not worth the writing, let alone the reading. And this is why so much bad poetry rhymes - because, bereft of meaning, the poet nonetheless wishes to make it clear that he is writing poetry, and not mere prose. But for all the rhyme in the world, bad poetry is just drivel, and no amount of rhyme can make it anything other than that.
Good poetry, rhyming or not, has a soul. Like music, it is something akin to a direct communication of feelings or ideas or insights from the writer to the audience, but as in music, it cannot be said to conform to no fixed rules; that it is merely an arrangement of words on the page. When that is attempted, chaos ensues, as we too often see in contemporary classical music, wherein composers seem to be writing only for the edification of other composers. Poets, true poets, write because they cannot not write, because they cannot keep silent. And the form in which they write is the most rarefied, the most sonorous, and the most ardent in all of literature. Good poets and good poems are linguistic treasures, and as with most treasures, they are extremely rare.