Within the Vidhiviveka, a Prābhākara-inclined Mīmāṃsaka debates with a Vedāntin about the meaning of Upaniṣadic sentences on the self.
The Prābhākara insists that all sentences should be injunctive in character, and that Upaniṣadic sentences should also be interpreted in this way. But what exactly could they prescribe? They could enjoin one to know their content, they suggest. But this option is not viable, since there is no difference between “s is p” and “you ought to know that s is p” insofar as one knows that s is p through the first sentence, too.
A further option would be that the Upaniṣadic sentences enjoin one to know their meaning in a definite way (niścaya), but this option is also ruled out. For, if the niścaya were obtained through language alone, then it would occur automatically, without the need to enjoin it. If it were not obtained through language alone, then it would occur because of something other than language, but then the Upaniṣads would no longer be the instrument for knowing about the ātman, which runs against other fundaments of the school.
At this point, the Prābhākara-like objector suggests a further possibility, namely that Upaniṣadic sentences prescribe arthaparatā, i.e., the ‘intentness on the meaning’. This also does not go, because prescriptions need to have preferably a visible purpose, like ritual prescriptions. And understanding sentences as aiming primarily at their meaning would put at a disadvantage exactly prescriptive sentences, which aim not only at conveying their meaning, but also at urging someone to perform a given activity. Moreover, a prescription should aim at a certain goal and knowledge cannot be a goal separated from the content to be known (as explained above with regard to the case of whether the understanding itself could be enjoined): ज्ञानस्य ज्ञेयाभिव्याप्तिफलत्वात् फलान्तरानभ्युपगमात्।