A neo-Aristotelian account of modal epistemology is one which is built on the idea of essences – that is, prior to both ontology and epistemology is a things real definition:
…one way to understand real definitions is to take them to be expressed by propositions which tell us what a given entity is or would be. (Tuomas Tahko, An Introduction to Metametaphysics, p. 163)
An essence is a things real definition – it is what it is, to put it another way. The cash value of this is basically that to know an essence is simply to know what a given thing is:
To know something’s essence is not to be acquainted with some further thing of a special kind, but simply to understand what exactly that thing is. This, indeed, is why knowledge of essence is possible, for it is a product simply of understanding, not of empirical observation, much less of some mysterious kind of quasiperceptual acquaintance with esoteric entities of any sort. And, on pain of incoherence, we cannot deny that we understand what at least some things are, and thereby know their essences. (Lowe, Two Notions of Being, p. 39, quoted in An Introduction to Metametaphysics, p. 164)
An interesting question for an epistemology of essence identified by Tahko is just how much of an essence do we need to grasp in order to have an accurate picture of its existence and identity? A question I would add is, does this leave room for error if we take ‘grasp’ to have a classical Aristotelian meaning, where the mind abstracts the universal from the particular. Another area where I’d question is exactly what the role of the empirical is here, especially when regarding natural kinds like gold – where does the a priori start and the a posteriori start, or vice versa? The above is clearly a priori and largely rationalistic, and so would bode well for modal epistemologies of, say, abstract objects (as well as counterfactuals, with which most modal epistemology is done), but what of actual, concrete objects, for which empirical data is needed? To what extent are our conterfactuals constrained by the empirical?
I don’t want to go so far as to say that we need an account of essences, at least in Aristotelian terms, because there’s a lot of metaphysical baggage there that can be questioned, but a neo-Aristotelian account of essence may certainly help as far as modal epistemology goes. Tahko goes on to suggest a combination of both a priori and a posteriori but is somewhat pessimistic about how well the distinctions actually serve here. The payoff here, however, is that an account of essences may serve to bolster a modal epistemology by combining the empirical with the rationalistic. Timothy Williamson suggests that ‘constitutive facts’ (basically, background knowledge that stays constant when we consider counterfactuals) may play an important role. Constitutive facts ‘fix’, as it were, our modal considerations by showing that any counterfactual without such a constitutive fact would generate a contradiction (gold having a different atomic number than 79, for instance). Tahko suggests that an account of essences would supplement an account of constitutive facts by showing us just what facts actually are constitutive – thus, we can think of essences as non-modal constitutive facts.