From Middle English affirmativeli, equivalent to affirmative +‎ -ly.

affirmatively (comparative more affirmatively, superlative most affirmatively)

1. In an affirming manner.
   • 1646/50, Sir Thomas Browne, Pseudodoxia Epidemica:

     For as the inference is fair, affirmatively deduced from the action to the organ, that they have eies because they see; so it is also from the organ to the action, that they have eies, therefore some sight designed; if we take the intention of Nature in every species, and except the casuall impediments, or morbosities in individuals.

   • 1603, Michel de Montaigne, chapter 12, in John Florio, transl., The Essayes[…], book II, London: […] Val[entine] Simmes for Edward Blount[…], →OCLC:

     When the Pyrrhonians say, that ataraxy is the chiefe felicitie, which is the immobilitie of judgement, their meaning is not to speake it affirmatively[…].

   • 1993 October, Nancy D. Polikoff, “Lesbian And Gay Parenting: What's At Stake?”, in Gay Community News, page 14:

     Many within our community view childrearing with skepticism or disdain. Affirmatively choosing parenting as a gay man or lesbian is often seen as a retreat from public activism to private life or as a mimicking of heterosexuality.

   • 2001, Bernard E. Harcourt, Illusion of Order:

     Order-maintenance proponents affirmatively promote youth curfews, anti-gang loitering ordinances, and order-maintenance crackdowns as milder alternatives to the theory of incapacitation and increased incarceration.