These lines have been taken from Eliot's one of the major essays, "The Metaphysical Poets"(1921) where Eliot is trying to establish the metaphysical school of poetry is the continuation of main stream of literature, not 'a digression from the main current'.

                 Dr. Samuel Johnson applied the term 'metaphysical' in his "The Life of Cowley" and referred to Donne, Cleveland and Cowley. Among them Donne and Cleveland mainly developed the concept of mixing 'heterogeneous ideas' as we find in Donne's "A Valediction:Fobidding Mourning". Here Donne compares the lovers to the "pair of compass". However the use of conceit is the main reason behind Johnson's opposition of metaphysical poets.

                     There is a Latin term, "discordia concors" which means disharmony in harmony. It suggests to the failure of conjunction or failure to combine or unite and Johnson says that metaphysical poets are failure in combining ideas, they just yoked two different ideas by violence.

               Johnson's allegations are true to certain extent. In Cleveland's some poetry we find some ideas are yoked by violence, but not united. Though Johnson sees it as a pejorative one, Eliot says that "a degree of heterogeneity of material compelled into unity by the operation of the poet's mind is omnipresent in poetry." Here we may refer to Eliot's "Tradition and Individual Talent"  where Eliot refers to the chemical analogy of two different things sulphur dioxide and oxygen which are forcefully combined by the temperature and by the present of the catalyst, platinum and they create a new thing, sumptuous acid.

          Actually poet's mind has its own ideas, ideals, and ideologies which unite the different ideas naturally. Eliot here means to say that which Johnson uses as a complain against metaphysical poets is not a matter of objection at all