Arnold's definition of poetry as a 'criticism of life' is an important post-Romantic articulation about the nature of poetry and its supposed relation with life. As different from the Romantic figuration which would foreground imagination over rationality, contemplation and realism, Arnold's definition works the way through a field of thought.
The definition is significant because it looks at poetry in a more realistic way than the Romantics and links the poetic faculty with the critical, something that Arnold's own authorial practice as both a poet and a critic demonstrates. It also argues in favour of the poets critical relation with the process of life that will remain his bedrock, all through. There is a universalism at work in the definition that finds application in works like Dover Beach.