In the grammar of English, the term do-support (or do-insertion) refers to the use of the auxiliary verb do, including its inflected forms does and did, to produce negated clauses and questions, as well as other constructions in which subject–auxiliary inversion is required. The verb do can be used as an auxiliary even in simple declarative sentences, where it usually serves to add emphasis, as in "I did shut the fridge." However in the negated and inverted clauses referred to above, it is used because the rules of English syntax permit these constructions only when an auxiliary is presen...