God is a properly basic belief
The argument is a core idea of reformed epistemology and has been advanced by various writers, including Alvin Plantinga and William Lane Craig. This view also agrees with presuppositional apologetics in that belief in God is axiomatic. Unlike reformed epistemology, presuppositionalism argues that all other beliefs depend on this axiom.
The argument hinges on a very particular interpretation of the practical understanding of the justified true belief model of knowledge. Even thought, the argument goes, the belief can only be viewed as inferable (rather than provable) from other truths, the view is justified on the basis that there are some epistemological systems in which the belief in God properly basic, where it is reasonable to accept it as a premise absent other evidence. Plantinga invokes the existence of other minds as a potential analogue:
- 'If we are justified, without other premises, in accepting the existence of other minds, we may be similarly justified in accepting the existence of a God. The claim "I am justified in believing that other minds exist" can be found to be true without any other premises. This claim is an instantiated claim. If we are permitted to treat an instantiated claim as properly basic, then there is some epistemological system in which the claim "I am justified in believing that there is a God" is true.
- Moreover, because my access to objective knowledge of true propositions is limited, that the proposition is justified is the only reasonable qualifier for whether a belief constitutes knowledge.'
There are two major moves in this argument; both are fundamentally Cartesian. The first is the move about whether or not the move to the existence of other minds is actually properly basic. The second is the move concerning pragmatic acceptance of propositions where we must hold some degree of skepticism, based on an inability to gain "objective knowledge" and whether or not that move is a good one.
Pragmatic acceptance of existential claims
Descartes' claims it is pragmatically necessary to accept the existence of other minds, provided we make certain assumptions about the nature of our own mind and perception. If we are to assume that there is some way in which the external world influences our perceptions (as opposed to a subjective entity) then it is reasonable to make certain assumptions about the presence of other bodies in space. There are ways to bootstrap this into an acceptance of other minds. In any case, it is often asserted that it is necessary to accept the existence of an external world on the basis that, regardless of the alternatives, we must behave as though the external world is the case.
However, Descartes' pragmatic assertion does not lend much strength to Plantinga's argument, because it is not really an assertion that the proposition needs to be properly basic, just that the proposition needs to be accepted at some level.
"God exists" is a synthetic proposition
One of the major concerns among epistemologists is what is considered acceptable as a 'properly basic' (or 'primitive') knowledge claim. Reformed epistemologists usually have strong ties to some version of Platonic epistemology. There are many other systems of epistemology, which are arguably more plausible than the Platonic system.
The Quine-ian approach to epistemology rejects the possibility that an existential claim can be properly basic, on the basis that existential claims are only cognizable through an understanding of categories; all category claims, then, are primitive to all existential claims. This argument was key in his attack on the ontological argument.
Kantian epistemologists assert that the only properly basic beliefs are analytic propositions. Reformed epistemologists generally reject Kantian epistemology, because the belief that God exists is classified is a synthetic proposition, and thus not viable to be seen as primitive.
Contemporary epistemologists in the line of W.V.O. Quine generally fall more or less in line with the Kantian method of thought when it comes to properly basic knowledge of instantiated propositions. Basically, it is considered irresponsible to speak of instantiations as properly basic. According Quine, only universal propositions (like tautologies) can be properly basic; knowledge of existential claims can only be derived through some sort of empirical method, and are expressed in terms of pre-existing general statements, like property-statements.