The topic is not explicitly discussed, as far as I know, in European or American epistemologists (who all seem to assume that it obviously is), whereas it is relevant in South Asian epistemology of language.
What makes a text a “commentary”? The question is naif enough to allow for a complicated answer. First of all, let me note the obvious: There is not a single word for “commentary” in Sanskrit, where one needs to distinguish between bhāṣyas, vārttikas, ṭippanīs, etc., often bearing poetical names, evoking Moons, mirrors and the like.
Suppose you want to undertake the study of Indian Philosophy and you want to read primary sources? Where should you start? I argued (in my contribution to Open Pages in South Asian Studies) that Bhaṭṭa Jayanta is a great starting point,
- Because he is a philosopher
- Because he deals with texts of other schools and thus aims at being understandable
- Because he is a talented writer
Well, yes… isn’t it?
The problem is less easy than it may look like and amounts to the problem of non-committal understanding. Is it the normal attitude while listening to a speaker or just an exception or an a posteriori withdrawal of belief once one notices that the speaker is in any way non reliable?