What's a properly epistemic difference?

There are different types of knowledge: mathematical, geological, biological, a priori, a posteriori, de se, interpersonal, hard-earned, esoteric, very well justified, professional, certain, firm, testimonial, propositional, etc.

When we divide up knowledge, some of the divisions are more properly epistemic than others. For instance, the difference between hard-earned knowledge and easy-come knowledge is not an epistemic difference at all—it is just a difference between how one came by it. If you and I live in villages on the opposite side of a mountain ridge, my knowledge of the waterfall outside our village is easy-come knowledge, while you had to work hard to earn that knowledge, climbing over the mountain ridge. But we are epistemically on par with respect to the knowledge of the waterfall. So, some types or classifications of knowledge do not divide up the knowledge epistemically at all. We might call these “wholly accidental” classifications of knowledge.

Other classifications of knowledge divide up the knowledge by means of the type of justification. For instance, the classic distinction between a priori and a posteriori is like this. Notice, however, that the very same thing can be known a priori and a posteriori. If you use a calculator to find out what 117 × 19 is, you learn it a posteriori, but if you use figure it out in your head, it’s a priori. And when the evidence is equal in strength and the content is the same, we do not have an epistemic difference to mark. (In the past, we might have said that a priori knowledge is better evidenced and maybe even infallible, but we now know that this is not in general true.) I am not sure whether the difference between a priori and a posteriori knowledge is a genuine epistemic difference. After all, the difference between knowledge gained by reading books in French and reading books in German doesn’t seem to be.

Yet other classifications of knowledge divide up the knowledge by the quality or degree of justification. Knowledge comes with better and worse justifications. This is a genuinely epistemic division.

The division of knowledge based on degree of certitude is ambiguous. By degree of certitude one could just mean a psychological feature of the agent, in which can this is not a properly epistemic division, or one could mean the degree of justification, in which case it is, or one could mean a combination of the two (“well-justified confidence”).

Another properly epistemic division of knowledge is with respect to content. Some differences of content do not seem to mark a genuine epistemic difference—say, the difference between biological and geological knowledge. But others do, like the difference between propositional and interpersonal knowledge do. At the same time, some of the content-based classifications include both an accidental and a properly epistemic element. Thus, it might be that interpersonal knowledge by definition must be gained through interpersonal interaction. But the epistemic benefits of interpersonal knowledge can be had without interpersonal interaction. So the concept of interpersonal knowledge may contain some epistemically accidental features about how the knowledge was in fact gained and some properly epistemic features as to the content.

This is all a bit of a mess.