"Fat Krishnadatta eats either during day or night. Fat Krishnadatta does not…

Concept

Arthapatti (presumption / postulation) is a means of knowledge in which, when an established fact cannot be explained without assuming a further fact, that further fact is necessarily postulated. The classic form supposes a disjunction of two possibilities and, finding one possibility ruled out, it presumes the only remaining one as the explanation.

Application

Here two exhaustive possibilities are given: the person eats by day or by night. One possibility is ruled out (he does not eat by day), yet a fact needing explanation remains (he must eat). The only way to account for this is to postulate the surviving possibility — that he eats by night. Inferring the unstated fact that alone makes the situation intelligible is exactly Arthapatti.

Contrast

• Upamana (comparison) gains knowledge of a thing through its similarity to something already known — there is no comparison of a known and unknown object here.

• Shabda (verbal testimony) derives knowledge from the reliable word of an authority — nothing here rests on someone's statement being trusted.

• Anupalabdhi (non-apprehension) establishes the absence of a thing from its not being perceived — this argument affirms a positive fact, it does not prove an absence.

Hence the reasoning is an instance of Arthapatti (implication / presumption).