Percy Bysshe Shelley's essay A Defence of Poetry has as it's main tenet the assertion, summed up in the concluding paragraphs, that poets are the force that drives society to higher and better planes; that poetic literature "has ever preceded or accompanied a great and free development of the national will." In accord with this, Shelley defends the poets of his era saying that "the literature of England ... has arisen as it were from a new birth" and that their own poetic age "will be a memorable one." He states:
It is impossible to read the compositions of the most celebrated writers of the present day without being startled with the electric life which burns within their words.
Shelley's essay has two parts. In the first, he defines "poetry in its elements and principles in terms of its connection with a "common source with all other forms of order and beauty." In this framework, Shelley further defines poetry as the mind acting upon the thoughts of reason to color those thoughts with the light of imagination, which is defined as the analysis of the relationship of things:
[Poetry may be considered] as mind acting upon those thoughts so as to color them with its own light, and composing from them ... within the principle of its own integrity.
In the second part, Shelley defends the then "present state of the cultivation of poetry" against those who were attacking the poetry of the Romantic Age as trivial in its self-centered focus on the poet's self-expression and reverence for the common elements of language and life, a self-centeredness also at one point criticized by Coleridge in Biographia Literaria. Shelley also defends his poetic peers idealization of "modern forms of manners and opinions," which led poets away from Aristotelian poetics toward a poetics inspired by nature and the poet's imagination instead of by divine influence. He further defends the poets' efforts to write poetry in accord with the new poetics based on self-expression, a idealization of common forms of life and language and poetic inspiration from the natural plane instead of the divine plane:
[Its] object an application of these principles to the present state of the cultivation of poetry, and a defence of the attempt to idealize the modern forms of manners and opinions, and compel them into a subordination to the imaginative and creative faculty.