Maṇḍana’s thesis is an answer to the problem of how to identify the core of a prescription. What makes people undertake actions? Kumārila’s śabdabhāvanā theory and Prabhākara’s kāryavāda had already offered their answers. Maṇḍana expands on Kumārila’s intuition about human behaviour being always goal-oriented by offering a radical reductionist hypothesis. According to this hypothesis, being a motivator is nothing but communicating that the action to be undertaken is an instrument to some coveted result. In this sense, prescribing X to people desiring Y is nothing but explaining that X is the means to achieve Y.
This cognitive interpretation of what motivates one to act could be accused of intellectualism. What about agents who, though understanding that X would be the appropriate course of action, do not undertake it, perhaps out of sloth?
A possible answer is that Maṇḍana’s theory describes the behaviour of ideal agents, who are able to evaluate rationally what is the best means to a coveted goal. Alternatively, one might suggest (as hinted at at the end of section 11.2) that even such irrational people would be impelled to act, even if they then do not physically undertake any act. The iṣṭasādhanatā is a motivator even for them, although they do not act correspondingly. One might think of the comparable case of someone who intensely desires an ice-cream and comes to know that great ice-creams are available in a given part of the city. They are ready to go there, but undergo an accident and are prevented from going. Although they do not practically act, the knowledge about the ice-cream shop did act as motivator for them.
Correspondingly, pravṛtti is used as a synonym of prayatna `effort’ and indicates the undertaking of an activity, not yet its realisation. Similarly, a person said to be pravṛtta is one who has already conceived the decision to undertake an action, although no movement can be seen yet.
(cross-posted on my personal blog.)