V. Eltschinger-III part

One of the main qualities of this book is that it stresses Dharmakīrti's statement that one needs a Sacred Text (in V.Eltsch.'s words: une Écriture) in order to initiate an activity. That is, although V.Eltsch. does not put it so explicitly, the other instruments of knowledge are reliable as far as the “material” world is concerned (I cannot pause here on the exact connotation that material would have in a Buddhist milieu and hope that the common sense understanding of it will suffice for the moment). They are reliable insofar as the description of the world as it is is concerned. But, they cannot tell one what he OUGHT to do. This thesis would be shared by Mīmāṃsakas, too. Hence, say the latter, the Veda has to be valid, otherwise there would be no key as to how to achieve (enduring) happiness. Buddhists, on the other hand, are content to say that the Buddhist texts, though not by themselves valid, are inferentially proven to be valid. My question is: where does the thesis of the non-derivability of the ought from the is derive from, within Indian Philosophy? In fact, it is not shared by, e.g., Naiyāyikas, who ground the validity of the Veda exactly in its epistemological validity insofar as our common world is concerned (namely, healing of poisons).