Philosophical definition of a poem, according to Samuel Taylor Coleridge(STC): What is poetry in kind and essence? According to STC a poem contains the same elements as a prose composition.
The difference between poem and prose is caused by the different combination of the elements because the aim of prose and the aim of poetry are different. The combination of various elements is a function of the difference of the aim of poetry and aim of prose. What could be the different objectives of a composition? The goal of a composition could be just to facilitate the recollection of given facts or observations by the arrangement of words and the composition will be a poem because it is distinguished from prose by metre or by rhyme or both jointly.
According to STC a composition that appears to be a poem because of rhyming words, while they do give a certain pleasure have only a superficial form of poetry. Communication of truths-- either absolute truths or demonstrable truths as in science or recorded as in history could be the goal of a composition. I think STC believes that it need not necessarily be the objective of poetry. I think STC believed that communication of pleasure or pleasure is the goal of poetry. Other kinds of compositions such as novels can bring pleasure too.
So pleasure is not the exclusive domain of poetry. Communication of pleasure may be the immediate purpose of works which do not have metre yet they are not poems but instead they are novels and romances. Can we add metre and rhyming words to a novel and make it a poem? STC's answer is that nothing can permanently please which does not contain in itself the reason why it is so and not otherwise. The definition of poetry that STC finally reached after these arguments is this: A poem is that species of composition which is opposed to works of science by proposing for its immediate object pleasure and not truth. Also poems as a whole give delight and the distinct parts of a poem give gratification. When reading a poem the reader should be carried forward not merely or chiefly by curiosity or by a restless desire to arrive at the final solution but by the "pleasurable activity of a mind excited by the journey itself." STC also said that poetry of the highest kind can exist without metre and even without the contra-distinguishing objects of a poem. The first chapter of Isaiah from the Bible, "indeed a very large proportion of the whole book is poetry in the most emphatic sense yet it would not be less irrational than strange to assert that pleasure and not truth was the immediate object of the prophet." STC addresses the question of if a poem of a certain length is all poetry. STC says that the question What is poetry? Is so nearly the same as what is a poet? That the answer to the one is involved in the solution to the other.
The question and answer in this post are inspired by the ideas in STC's Biographia Literaria.
