They desired simplicity of style.
When the _Lyrical Ballads_ of Wordsworth and Coleridge were published in 1798, the preface which Wordsworth wrote as their manifesto hardly touched at all on the poetic imagination or the attitude of the poet to life and nature.

The only question is that of diction.

"The majority of the following poems," he writes, "are to be considered as experiments.
They were written chiefly with a view to ascertain how far the language of conversation in the middle and lower classes of society is adapted to the purposes of poetic pleasure." And in the longer preface to the second edition, in which the theories of the new school on the nature and methods of the poetic imagination are set forth at length, he returns to the same point.

"The language too, of these men (that is those in humble and rustic life) has been adopted ...

because such men hourly communicate with the best objects from which the best part of language is originally derived, and because from their rank in society, and the sameness and narrow circle of their intercourse, being less under the influence of social vanity, they convey their feelings and notions in simple unelaborated expressions." Social vanity--the armour which we wear to conceal our deepest thoughts and feelings--that was what Wordsworth wished to be rid of, and he chose the language of the common people, not because it fitted, as an earlier school of poets who used the common speech had asserted, the utterance of habitual feeling and common sense, but because it is the most sincere expression of the deepest and rarest passion.