In the modern perspective, we normally think of poetry as anything that is written in verse. Aristotle’s definition is more specific. Aristotle states that poetry is a kind of imitation that employs language, rhythm, and harmony. These elements are certainly present in most poetry, though there are notable differences.

The first difference is that Aristotle makes no requirement that poetry be written in verse. As long as it has rhythm and harmony, prose could qualitfy as poetry. While this difference tends to be more inclusive, the second one is more limiting.

The second difference is that in claiming that poetry is imitative, Aristotle limits poetry to narrative. In other words, it has to describe something in the world. This would exclude most abstract or experimental poetry of the past century, and would also raise serious questions about the dominant tradition of lyric poetry in the modern world. This is because lyric poetry usually deals more with emotions and ideas than with events and actions.