This question uses Indian logic (Nyaya). The invariable connection between the middle term (hetu, e.g. smoke) and the major term (sadhya, e.g. fire) is called vyapti (pervasion). Vyapti can be established two ways: anvaya (agreement in presence: wherever the middle is, the major is) and vyatireka (agreement in absence: wherever the major is absent, the middle is absent).

The question asks for the argument where the middle term is always positively related to the major, with no negative instances of agreement in absence. That describes a purely affirmative (kevala-anvayi) inference — one where the major term is present everywhere, so there can be no negative example to show absence.

Consider the reasoning: "All knowable objects are nameable. The pot is a knowable object. Therefore the pot is nameable." Here everything whatever is both knowable and nameable — there exists nothing that is un-nameable, so no negative instance of absence can ever be found. The relation is only affirmative (anvaya alone), matching the description exactly.

The smoke-and-fire and non-fiery examples all rely on genuine negative instances (kitchen has both fire and smoke, a lake has neither) — they use vyatireka, agreement in absence, so a negative instance does exist. The earth-and-smell argument likewise depends on contrast with things lacking the property. Hence only "All knowable objects are nameable; the pot is a knowable object; therefore the pot is nameable" is the purely affirmative inference with no negative instances.