Talk:Do-support/Origin

Uses of do in Old English include:
 * 1) lexical. a full lexical verb, often replacing another verb: "Let us do [= put] him in this old well"
 * 2) substitutional. a substitution for another verb elsewhere in a clause: "...he killed many more in death than he did before [when he was alive]"
 * 3) causative. "And trees he does [= causes] to bloom suddenly and again to wither quickly"

These uses continued into Middle English; however, the use of auxiliary and modal verbs was expanding greatly at the same time. In this environment, the use of do as an auxiliary verb in periphrastic constructions, in addition to its existing uses in Old English, arose in response to a gap in the developing auxiliary system.

In fact, it is generally accepted that this periphrastic use of do, the basis of do-support, evolved from one of these uses inherited from Old English. While linguists have at times mooted theories positing each use (lexical, substitutional, or causative) as the origin of do-support, causative do now has widespread support as the progenitor.