Consider the following epistemological argument against Naturalism (as defined below):
- If Naturalism is true, then all factual knowledge (i.e., knowledge of facts) is acquired empirically.
- Knowledge of necessary facts cannot be acquired empirically.
- We have some knowledge of necessary facts.
- Therefore, Naturalism is not true.
The insights behind the argument aren’t original to me, but the formulation is mine. Before I defend the three premises, let me clarify the key terms used in the argument.
Naturalism refers to the ontological thesis that only natural things exist, that is, things that exist spatiotemporally and can be described according to our best physical theories. On this definition, Naturalism is roughly equivalent to physicalism, the view that the fundamental ‘stuff’ of reality is physical and whatever exists can be accounted for (in principle) in terms of physical reality (physical particles, physical forces, etc.).1
Factual knowledge refers to knowledge of facts about the world; specifically, facts about an external world that exists independently of our minds. Factual knowledge is distinct from (1) analytical knowledge (i.e., knowledge of logical or conceptual truths, such as that a triangle is a polygon) and (2) knowledge of internal mental states (e.g., that I am currently experiencing pain). A simple example of factual knowledge would be that there are, at this present moment, more than two turtles in Turtle Pond.
Empirically means by way of sense experience or observation, that is, by means of our sensory organs (the standard five senses or any others we might have that operate on a similar basis).
Necessary facts are facts about what must be the case, as opposed to what merely is the case or could be the case. To know a necessary fact is to know not merely that something actually is the case, but also that it could not possibly have failed to be the case. Knowledge of necessary facts is a species of factual knowledge (as defined above).
Now, back to the argument. I think it’s fairly clear that the argument is logically valid: the conclusion follows from the three premises. If premises 2 and 3 are true, it follows that some factual knowledge is not acquired empirically, in which case — by modus tollens from premise 1 — Naturalism is not true.
So why think that the premises are true? Consider each in turn.
- The physicalism could be reductive or non-reductive; I don’t think it makes a difference to the argument. Some self-professed naturalists hold to a more liberal ontology, e.g., allowing for sets or abstract mathematical objects. Whether those more liberal versions of naturalism are vulnerable to this argument is an open question that I won’t address here. ↩