Wordsworth wrote his introduction as a way of explaining why the poems in "Lyrical Ballads" were so different from popular poetry that had come before. As he says, there has been a general expectation that people who write in verse make a kind of "promise" to their readers that certain...
Wordsworth wrote his introduction as a way of explaining why the poems in "Lyrical Ballads" were so different from popular poetry that had come before. As he says, there has been a general expectation that people who write in verse make a kind of "promise" to their readers that certain themes will be handled in a specific manner and that other themes will be excluded -- that poetry will deal with "noble" themes using exalted language. "Lyrical Ballads" defies those expectations. Wordsworth lays out how different his project is in one remarkable sentence:
The principal object, then, proposed in these Poems was to choose incidents and situations from common life, and to relate or describe them, throughout, as far as was possible in a selection of language really used by men, and, at the same time, to throw over them a certain colouring of imagination, whereby ordinary things should be presented to the mind in an unusual aspect; and, further, and above all, to make these incidents and situations interesting by tracing in them, truly though not ostentatiously, the primary laws of our nature: chiefly, as far as regards the manner in which we associate ideas in a state of excitement.
The principle features of Wordsworth's idea of poetry are that its subject matter should be incidents from common life; that the language of poetry should be the language of common men; that poetry is the product of an excited state of imagination; and that the essential theme of poetry is the representation of these events in such a way as to show how they represent the common laws of nature.
I think the main significance of Wordsworth's formulation is that, with the Romantics, poetry becomes a private and personal form of discourse; Wordsworth's allusion to the "promises" earlier poets made to their readers had to do with the expectation that poetry was a high form of public discourse. With "Lyrical Ballads," poems that Wordsworth feared were "so materially different" from what the public liked, the proper subject for poetry becomes the personal, or the emotional and imaginative inner landscape of the poet.