Let us say that a belief is justified for a person at a time if (a) he is violating no epistemic duties and is within his epistemic rights in accepting it then and (b) his noetic structures is not defective by virtue of his then accepting it. [Alvin Plantinga, "Reason and Belief in God," in Alvin Plantinga and Nicholas Wolterstorff, eds., Faith and Rationality: Reason and Belief in God (Notre Dame, IN: University of Notre Dame, 1983), 79]
"Reformed Epistemology" is a system that claims to be based upon truths in the Reformed tradition, particularly as articulated by John Calvin. In a short article dealing with the existence of God as a properly basic belief, Alvin Plantinga wrote against Classical Foundationalism and introduced his idea of properly basic beliefs, of which the existence of God is one of them. In this post, I would like to deal with Plantinga's twin criteria for justification of beliefs.
Plantinga's criteria for justification, as presented here, deal with a person's epistemic duties and a working noetic structure. I would definitely agree that one should hold to be true what is congruent with the other truths one holds to, and thus one ought to not violate his epistemic duties, but that does not help us deal with foundational beliefs, for we are just beginning to ascertain what actually are foundational beliefs. As examples of properly basic beliefs, Plantinga brings up beliefs that one acquires through sense experiences like "I see a tree," but these circumvent the issue of whether the senses are indeed reliable. Whether the senses are generally reliable or not reliable is something that has not been decided yet in the building up of one's epistemology; one cannot assume they are generally reliable from the start unless one is an empiricist (and empiricism is wrong since empiricism itself is not empirically proven to be true).
Now, of course the question might be posed as to why anyone should want to believe that the senses are unreliable. But that is besides the point here. Most people will agree, as do I, that the senses are generally reliable. But one could believe that the senses are generally reliable because of other prior beliefs that are deemed to be more basic. In other words, it is not the case that those who do not accept sense experiences as foundational would therefore distrust the senses. Thus, to posit the criterion that one's noetic structures are not defective by virtue of accepting a belief is to beg the question. How exactly does one define whether one's noetic structures is or isn't defective?
Plantinga's justification criteria for properly basic beliefs are, in this sense, properly basic, yet totally worthless. They are true to the point of tautologies, yet worthless for judging whether any belief X is properly basic, since one cannot know if one is actually violating one's epistemic duties or if one is having a defective noetic structure by holding to belief X. One can be subjectively justified to be sure, sure that one has actually fulfilled those criteria, but since the question of whether belief X truly and objectively conforms to the criteria remains, one can never be objectively justified in holding to any "properly basic belief."