• Warranted Christian Belief (2000)
• Warrant and Proper Function (1993)
• Warrant: the Current Debate (1993)
• Does God Have a Nature? (1980)
• God, Freedom & Evil (1974)
• The Nature of Necessity (1974)
• God and Other Minds (1967)
He is famous for his Reformed Epistemology in which he claims that belief in God is warranted or justified without any evidence. In other words, it is just as properly basic for man to believe in God as it is for man to believe in other minds or in the reality of the past (i.e., memories). He argues that this belief in God is a result of the sensus divinitatis (sense of the divine) which is found in each man (apparently based on Romans 1:19-21).
Although he is extremely erudite and his tomes demonstrate the highest of scholarship, when you actually "boil down" what he is saying, it comes down to: Belief in God just seems right (based on the reliabilist theory of knowledge).
See the first few minutes of the following video clip:
While technically Reformed Epistemology would allow for the basic belief in God to be defeated if the right evidence surfaced, practically speaking, it doesn't appear that Plantinga would really give up his belief. He writes:
...it is possible, at any rate in the broadly logical sense, that just by following ordinary historical reason, using the methods of historical investigation endorsed or enjoined by the deliverances of reason, someone should find powerful evidence against central elements of the Christian faith; if this happened, Christians would face a genuine faith-reason clash. A series of letters could be discovered, letters circulated among Peter, James, John, and Paul, in which the necessity for the hoax and the means of its perpetration are carefully and seriously discussed; these letters might direct workers to archaeological sites in which still more material of the same sort is discovered . . . . The Christian faith is a historical faith, in the sense that it essentially depends upon what did in fact happen: "And if Christ has not been raised, your faith is futile" (I Corinthians 15:17). It could certainly happen that by the exercise of reason we come up with powerful evidence against something we take or took to be a deliverance of faith. It is conceivable that the assured results of HBC [Historical Biblical Criticism] should include such evidence. Then Christians would have a problem, a sort of conflict between faith and reason.So, it seems that he doesn't think it even remotely possible that some defeater could surface but in the unlikely event that it did, he doesn't know what he would do. I predict he would continue to hold on to his belief and find a way to explain the new evidence to agree with his faith.
However, nothing at all like this has emerged from HBC, whether Troeltschian or non-Troletschian; indeed, there is little of any kind that can be considered "assured results," if only because of the wide ranging disagreement among those who practice HBC. We don't have anything like assured results (or even reasonably well-attested results) that conflict with traditional Christian belief in such a way that belief of that sort can continue to be accepted only at considerable cost; nothing at all like this has happened. What would be the appropriate response if it "did" happen or, rather, if I came to be convinced that it had happened? Would I have to give up Christian faith, or else give up the life of the mind? What would be the appropriate response (emphasis mine)? Well, what would be the appropriate response if I came to be convinced that someone had given a wholly rigorous, ineluctable disproof of the existence of God, perhaps something along the lines of J. N. Findlay's alleged ontological disproof? Or what if, with Reid's Hume, I come to think that my cognitive faculties are probably not reliable, and go on to note that I form this very belief on the basis of the very faculties whose reliability this belief impugns? If I did, what would or should I do--stop thinking about these things, immerse myself in practical activity (maybe play a lot of backgammon, maybe volunteer to help build houses for Habitat for Humanity), commit intellectual suicide? I don't know the answer to any of these questions (emphasis mine). There is no need to borrow trouble, however; we can think about crossing these bridges when (more likely, if) we come to them (Warranted Christian Belief, pp. 420-421).
Plantinga also makes another very interesting admission. He acknowledges that his epistemology could be applied to confer warrant for other religions such as Islam (Warranted Christian Belief, p. 350 and Faith and Rationality: Reason and Belief in God, eds. Alvin Plantinga and Nicholas Wolterstorff, p. 78). So, his argument for a properly basic belief in God does not uniquely apply to Christianity.
He also uses a somewhat strange argument to counter the logical problem of natural evil. He says that natural evil could be caused by demons (God, Freedom, and Evil, p. 58). While he offers this only as a potential solution to defeat the logical problem of evil, nevertheless, it sounds more like a Medieval philosopher than it does one of the brightest lights of the modern era in philosophy.
So, while many today are enamored with Reformed Epistemology and the philosophy of Alvin Plantinga, I am not one of them.
For some excellent criticisms of Plantinga's Reformed Epistemology see, Matt McCormick, Finding God in My Own Mind
Jaco W. Gericke, FUNDAMENTALISM ON STILTS: A RESPONSE TO ALVIN PLANTINGA’S REFORMED EPISTEMOLOGY
Erik Baldwin, Could the Extended Aquinas/Calvin Model Defeat Basic Christian Belief ? (Philosophia Christi, Vol.8, No. 2 2006)
For a layman's summary of Baldwin's paper see the series on Common Sense Atheism
Evan Fales interview on Common Sense Atheism