Maṇḍana was a key thinker within Sanskrit philosophy and possibly the first one to introduce the genre of thematic monographs dedicated to specific topics.

In his monograph on prescriptions, he implemented a revolutionary approach to deontics, interpreting prescriptions as sheer descriptions of state of affairs, namely the instrumentality relation holding between the seemingly enjoined action and the agent’s desired result. “Do X if you desire Y” is therefore nothing but “X is an instrument to Y”.
Similarly “Don’t do X” is nothing but “X is an instrument for an undesirable outcome”. However, in the case of prohibitions, the undesirable outcome is incommensurably greater than any possibly reachable desired output.

In this way, he could achieve multiple goals (in increasing order of importance for Maṇḍana),
1. treat prescriptive statements as if they were descriptive, thus allowing for a smooth interaction among them,
2. make space for non-prescriptive statements in the Vedas (wheras Kumārila and Prabhākara claimed that the Vedas contain only prescriptive statements),
3. allow for a general theory of human motivation as based on rationally conceived goals.

At the same time, Maṇḍana did not want to break up with the previous Mīmāṃsā tradition and its distinction among three types of duties. His reduction might have led to the conclusion that all duties are just based on instrumentality and have therefore no different degree of obligatoriness, but Maṇḍana’s attempt was based on the idea that instrumentality was the real core of the notion of obligatoriness, not an alternative notion. Thus, it should have been able to make sense of the entire Mīmāṃsā deontic building.
Consequently, Maṇḍana kept fixed duties as fixed, but needed therefore something to be fixedly desirable as their coveted result. What could this have been? Maṇḍana discussed and eliminated various options. Happiness, for instance, would not be enough, because though people generally desire happiness, they might be too lazy to undertake cumbersome actions to achieve it. By contrast, reduction of pain is considered to be a universally desirable output and one which would motivate even lazy agents. Thus, Maṇḍana settles for reduction of bad karman as the output of fixed duties, because of the present unpleasant outcomes of bad karman (such as present suffering) and because bad karman will hinder one’s future enterprises. In this way, Maṇḍana could distinguish between elective duties (bound to specific desires and outputs) and fixed and conditional ones (bound to the reduction of bad karman, which is generally desirable).

The core of his solution for the Śyena problem centers on the rationality of the agents involved: No one would want to obtain a small benefit in exchange for the negative output (the always undesirable bad karman) of transgressing a prohibition.

Even though later Mīmāṃsā authors generally disagreed with Maṇḍana’s solution, they often incorporated some elements of it within their own schemes (e.g., the Bhāṭṭa Mīmāṃsā Pārthasārathi incorporated the awareness of instrumentality in his teaching of prescription, see Freschi 2012). Several Vedāntic schools also took advantage of his solution for justifying their reading of the Vedas as (also or chiefly) descriptive.