Devadatta is fat. He does not eat during the day. The two observations together are incoherent without a third fact: Devadatta must eat at night. The Mimamsakas argue that the third fact is known, by its own cognitive route. There is no perception of it. There is no general rule from which it has been inferred. What forces the knowledge claim is the requirement that the observed facts cohere.
This is arthapatti - postulation from inexplicability. A distinct pramana, separate from perception, inference, comparison, testimony, and non-perception. Its operational shape is specific: an observation generates a knowledge claim by demanding what is necessary for its own coherence. The unstated is implicated by the structure of the stated.
Two forms are distinguished. Drshtarthapatti - postulation from perception - runs from observed facts that cannot stand alone (Devadatta’s case). Shrutarthapatti - postulation from testimony - runs from utterances that would be incoherent unless some unstated fact is in play. Both share the same logical signature: an observed fact, an inability to stand on its own, and a postulated fact called forth by the coherence requirement.
Where English Falls Short
The closest English term is abduction (Peirce) - inference to the best explanation. Abduction is comparative: among available explanations, pick the one that best explains the observation. Arthapatti is constrained more sharply. It operates when the observation cannot stand on its own at all; the postulated fact is the one that makes the observation coherent, not merely the most probable explanation. Abduction asks “what is the most likely explanation?” Arthapatti asks “what must be true for this to make sense as stated?” The difference is between probability and necessity.
Presupposition in linguistics is a related concept - what an utterance requires to be true for it to be interpretable. Arthapatti is broader: presupposition is a property of utterances; arthapatti is a method of arriving at unobserved facts about the world from the coherence requirement of any observation, not only of utterances.
Where it Shows Up
Debugging AI output. A model produces a response that does not cohere with the prompt as written. What hidden context must the model have access to, or be inferring, for this output to make sense? The arthapatti move traces to the unstated assumption - often a system prompt, a memory, or an inference the prompter did not realize was in play.
Reading institutional decisions. Leadership announces a decision with a public rationale that does not hold together. What must be true, and unstated, for this decision to be sensible? The unstated is then known, with appropriate force, by the necessity of coherence.
System behaviour analysis. A system behaves contrary to spec, and the behaviour is reproducible and patterned. What hidden state must be present for the behaviour to make sense? The hidden state is implicated by the coherence requirement.
Reading user behaviour. A user does X and then Y, and the two are incompatible given the stated user goal. What unstated goal would make both coherent? Arthapatti drives the reframing.
Evaluating model performance claims. A model is reported to perform at a certain level. The reported performance is inexplicable given the model’s known capabilities. What unstated factor - data leakage, prompt structure, evaluation framing - must be in play for the performance figure to be coherent?
IKS Roots
The Sanskrit term is arthapatti (अर्थापत्ति), literally “the falling-in of meaning” or “implication of an object,” from artha (meaning, object) + apatti (falling into, entailment). The Bhatta school of Mimamsa (Kumarila Bhatta, 7th century) defends it as an independent pramana; the Prabhakara school agrees, with technical differences. Nyaya subsumes the move under anumana, arguing the postulation is a form of inference with an implicit pervasion. The Mimamsakas respond that the cognitive structure is different - no instance from which a pervasion has been generalized is in play; the route is the necessity of coherence itself. The dispute about whether arthapatti reduces to anumana or stands independently is one of the central technical debates in Indian epistemology.
See also N1 (the wider system of pramanas) and N2 (vyapti - the structure of inference, which arthapatti is structurally distinct from on the Mimamsa account).
Further Reading
Kumarila Bhatta’s Slokavartika, the arthapatti section, with Parthasarathi Misra’s commentary. The Karl Potter Encyclopedia of Indian Philosophies volume on Mimamsa for a scholarly entry. Stephen Phillips, Epistemology in Classical India, for an accessible introduction.