One of the main argumentative techniques that Shelley uses contrast. At the beginning of “A Defence of Poetry,” Shelley defines imagination and reason. He then contrasts these ideas against each other. They are both courses of mental action, but reason contemplates things while imagination takes the contemplated thoughts and connects them.

Shelley also contrasts the broad definition of poetry against the narrow definition of poetry. First, Shelley defines poetry as all works of imagination, and he includes the traditional form of poetry in that. Then he goes deeper, distinguishing poetry as a form of writing with language, meter, and rhyme. He contrasts this narrow definition with the broader definition of poetry being any work of imagination, and in the contrast, the written poetry is revealed to be the superior art form. In his narrow definition, poetry comes from pure imagination because it is language, as opposed to other works of art, which are composed from other created materials. Contrasting the different types of poetry makes his terms clearer and his argument stronger.