Śālikanātha discusses the definition of a source of knowledge (pramāṇa) at the beginning of his Pramāṇapārāyaṇa and analyses various criteria.
First of all, he discusses the criterion of avisaṃvāditva ‘non deviation’ (used by Dharmakīrti and his school) and shows how this is not enough to exclude memory (smṛti). Dharmakīrti could exclude memory because it is conceptual, but this would exclude also inference (anumāna).
Next suggestion (again from Dharmakīrti’s school): using causal efficacy (arthakriyā) as criterion. But in this way memory should again be considered a source of knowledge, since it can be causally efficacious. One could say that, unlike in memory, in the case of inference there is a connection (though indirect) with the object. But this, again, applies to memory as well!
A new attempt is to say that a source of knowledge is identified insofar as it leads to know something unknown (aprāptaprāpaka), which is a criterion typical of Kumārila. A variant thereof is to say that it causes to act people who were previously inactive (pravartakatva), but this would lead to the fact that non-conceptual cognitions (nirvikalpa) would not be sources of knowledge, given that they cannot promote any action.
Why not using aprāptaprāpaka as criterion? Because this would not apply to the case of continuous cognitions (dhārāvāhikajñāna). These are cognitions like the ones originated out of continuously looking at the same object. These count, according to Śālikanātha, as sources of knowledge, but would not be such if the criterion of aprāptaprāmāṇaka were to be the defining one.
What about dṛḍha ‘sure’ as criterion, then?
Here Śālikanātha can give voice to the Prābhākara theory of knowledge. First of all, he asks, what would dṛḍha exclude? If it excludes doubt, then this is wrong, since there is no doubtful cognition. What we call ‘doubt’ is instead the sum of two distinct cognitions (readers might want to recall the fact that for the Nyāya school, doubt is a cognition in which two alternatives are exactly equally probably).
As for erroneous cognitions, these also don’t need to be excluded from the definition of knowledge, because there are no erroneous cognitions. What looks like an erroneous cognitions, is at most an incomplete one. For instance, mistaking mother-of-pearl for silver means rightly recognising a shining thing on the beach + remembering silver. The latter part is not knowledge, but just because it is memory. Śālikanātha similarly treats the case of jaundice and other perceptual errors.
His conclusion is a minimal definition of knowledge: pramāṇam anubhūtiḥ “knowledge is experience”.