Pure nature defined negatively: nothing added, good or bad, beyond what is owed
Jansenius, already mentioned, reports and explains the scholastics' view on this in book 1, chapter 1 of On the State of Pure Nature. On their account nature is called pure by a negative purity: nothing is added to it, good or bad, beyond what is owed to it. It has neither sin, nor the punishment that goes with sin, nor any gift of grace beyond nature.
Latin
XVIII. Nam ut mentem Scholasticorum hac in parte refert & explicat jam dictus Jansenius, de statu naturae purae libro primo capite primo, juxta illos, pura natura dicitur puritate negativa, quia scilicet, nihil habet superadditum sive bonum, sive malum, quod ei debitum non sit: ita neque peccatum habeat, poenamque peccati comitem, neque ullum gratiae naturam superantis donum.