What makes a poem a poem?
A poem can achieve a variety of purposes--tell a story, describe a scene, develop a theme, share an insight, express an emotion, ask a question. The common element in poetry that pulls each of these into the genre is the use of connotative vs. literal language and the employment of figurative language. Thus we find passages of "pure poetry" in many novels. (I think of Fitzgerald and Steinbeck here in their descriptive writing.)
In my teaching experience, students who think in very literal terms have difficulty developing an appreciation of poetry. To them poetry is written in a foreign language.
In short, what makes a poem a poem is the ability to make the reader feel something. I know that can happen with prose, as well, but it seems to me it must happen with a poem. As has already been mentioned, a poem is different in form from prose--the normal rules of writing just don't apply. That doesn't mean a poem can't have form or punctuation, but it doesn't have to. One of the books I teach from is called Sound and Sense, which comes from the idea that poetry should match its sound with its meaning (sense). If it's a serious or depressing poem, the language should reflect that. If it's a poem about how long something should take, the words should not be short and move wuickly over the tongue. I suppose, in the end, a poem is anything which is not prose.
I used to think poems had to rhyme to be poems, but that's not the case at all! To me, poetry is using words to draw a picture in the reader's mind. It's putting words together to transport the reader to another time and place. It's the art of saying a lot without using a lot of words or taking up a lot of space. It's the spirit, or soul, of mankind reaching out to others through well placed words or phrases.
Poetry either inspires us or depresses us! It can lift us up on the highest pinnacle of the highest mountaintop, or it can dash us to pieces on the rocks! Even Biblical characters wrote in poetry, as we find in Psalms and Proverbs. Anybody, anywhere, anytime can read, enjoy, and write poetry.
I think a poem attempts to say the most while saying the least, and perhaps we as readers can recognize this unique art form when we read certain passages by certain authors, like someone mentioned about Steinbeck and Fitzgerald.
It's rather easy to recognize poetry when it's fed to us in stanza form, when it rhymes, when we recognize similes and metaphors, etc., but we all know that great poetry can be created without such devices. I think, though, at its essence, poetry is a form of literary expression in which the poet uses literary techniques that can effectively express a message that can be interpreted differently by various readers.
I think in order to "define" poetry, you have to look at a piece of writing in comparison to prose. Prose can be loosely defined as written work whose basic unit (building block) is the sentence. Poetry can be loosely defined as written work whose basic unit is the line. In comparison to prose, poetry is often written in elevated language. Good poetry is said to be "held" on its images.
But I agree with the first post. This question is open to many interpretations, and they will all be based on opinion and experience. Think of how many pieces of writing that have been thought of as prose have been described as "poetic." Think of how many poems (like epics) tell elaborate stories and can be read like novels.
Outside of grammar, there are no hard and fast rules in defining written works. This is what makes English/literature so different from science and math. This is also what makes those of us who teach English, love it.
This one will receive many responses and might be moved to the discussion realm. There might be definitive definitions with strict limiting functions about what constitutes a poem. I would say that while these can be used and while they have their own criteria, I believe that a poem is defined by having something to say. I think that the element of a statement being made or asserted is of vital importance in the definition of a poem. In my mind, a poem can be about anything, nothing, something, but it must have an element of a declarative nature about that entity. Even if it seeks to not pose an answer, but merely open with successive questioning, I believe that this is a statement in its own right. These elements can be critical in defining a poem. When I reflect on what poems help to define the genre, I would say that the ability to make statements, to forge connections behind these particular elements are of vital importance in helping to construct the elements of a poem. As with all poetry definitions, it is going to be helpful for you to keep an open mind and focus on the different conceptions of a definition that you will receive on such a broad topic.
This is one of the most difficult questions to answer. Poetry is one of the purest of literary genres so much so that all generic codes get collapsed in it. What constitutes poetry? I will give my very personal opinion.
When does a linguistic statement become poetic? I would say it becomes poetic by evoking a striking image, by investment of feelings and through some profound observation. If we say--"I moved the pen from the right to the left", it is a statement but when I say--"I moved the pen from the right to the left like a magic wand/But did it make any difference to the centre of the earth?", it is the similitude between the pen and the wand and the relation between its movement and some change in the centre of the earth that make us think and imagine the connections implied. Poetry should always create an imaginative space like that either at the level of its content or its form or a deviational use of language.