ثم لا نسلم انتفاء التخصيص
Furthermore, we do not concede that restriction is absent.
Rejecting a proposed condition or reconstruction does not prove that every possible type of restriction has disappeared. The speaker may still contrast a particular person, category, or degree in a way not captured by the initial grammatical account.
Conversely, a merely possible contrast does not establish a certain restriction. The object of restriction and the competing alternative must both be specified before confidently assigning qaṣr.