Alvin Plantinga is a professor of philosophy at the University of Notre Dame most known for his Christian apologetics and defenses of dualism and free will. Like much apologetics, his work in this area repackages many age-old arguments. In Plantinga's case, he has reformulated many arguments from the Reformed (Calvinist) tradition such as sensus divinitatis. He also has no understanding whatsoever of evolution and considers his lack of understanding constitutes making important points.
Plantinga's significance in contemporary analytic philosophy stems from his work in epistemology contained in three books: Warrant: The Current Debate, Warrant and Proper Function and Warranted Christian Belief. In these three works, Plantinga builds up a theory that attempts to provide a framework for answering the question: for the beliefs we have, to what degree are we warranted?
The first book, Warrant: The Current Debate explains the basic premise of this inquiry and why the terminology of warrant is preferred over other epistemological terms (broadly, because Plantinga believes that a lot of other terms used to signify this state of positive epistemic status presume the conclusions they seek: for instance, saying warranted beliefs are justified presumes that an account of beliefs being based on justification is the correct epistemological theory).
Plantinga presents a variety of answers from the epistemological literature but finds fault with them because of their failure to deal with the challenge of "cognitive malfunction". Needless to say, the counter-examples he presents are hypothetical and speculative rather than medically accurate. In Plantinga's view, a theory must be able to all possible logical counter-examples (even if the scenarios described in those counter-examples are physically impossible in the actual universe we live in, or indeed highly improbable).
As the philosopher Tyler Wunder notes, at the end of Warrant: The Current Debate, Plantinga shifts his standard of evidence before he presents his own theory:
What I propose to explain and explore is our notion of warrant, a notion nearly all of us have and employ in our everyday pursuits. This notion is not best explained, I think, just by producing a set of severally necessary and jointly sufficient conditions. Such a procedure is at home in logic and mathematics; it works somewhat less well or less directly in, say, the metaphysics of modality, and it works still less well (or still less directly) in epistemology. What we really have are paradigms: central, clear, and unequivocal cases of knowledge and warrant. But there is also a sort of penumbral zone of possible cases surrounding the central cases; these cases don't conform exactly to the conditions characterizing the central cases, but are instead related by way of analogical extension and similarity. And there is an even more shadowy belt of possible cases beyond that one, an area that is constituted by borderline cases, cases where it is not really clear whether what we have is knowledge (warrant) or not. More exactly, there are borderline cases between the central paradigmatic cases and those comprising the analogical zone, and borderline cases between the latter cases and cases that are not cases of warrant at all.
Plantinga insulates his theory from the challenge of having to satisfy all possible logical counter-examples by setting a new standard... but doesn't apply that standard to the theories he's already rejected. Sneaky.
Warrant and Proper Function presents Plantinga's theory of warrant, which he describes as a theory of "proper function". The theory is used in the book to jumpstart an argument against naturalism: namely, that if one is attracted to Plantinga's theory, it is—Plantinga says—very hard to square with a naturalistic understanding of evolution if you don't presume that there is a God.
Warranted Christian Belief applies Plantinga's account of warrant to religious—specifically Christian—beliefs. Plantinga comes to the somewhat startling conclusion that religious believers have a built-in module for believing in God, a sensus divinitatis. Belief in God is thus justified as a "properly basic" belief in the same way that perceptual beliefs about the world around us are—because believers get a direct knowledge of God through the sensus divinitatis, much as we get direct experience of the visual world through our eyes. Pesky atheist types don't get any such experience because of the "noetic effects of sin". Which is very convenient.
 Some arguments for and about God
 God as basic belief and necessary being
Plantinga argues that God can be accepted without proof just as the existence of other minds can - what is called a "basic belief", that is axiomatic. A skeptic of the analogy to the existence of other minds would argue that this isn't actually taken on faith. That another mind exists inside another human being is a strong inference based on outward observations, as humans pass the Turing test (or at least should pass). The fields of psychology, cognitive science, and neuroscience make it possible to extend basic observations to looking at the structure of the brain and the isomorphism between that physical structure and the human mind - all evidence that makes it highly unlikely that other minds don't exist. The existence of God, specifically any Judeo-Christian one that Plantinga supports, isn't taken based on this sort of evidence.
In response to Richard Dawkins' "god hypothesis" assertion that God must be complex, he suggests that God, being spiritual in nature, is in fact simple - simple enough to be axiomatic.. Russell Blackford, among others, disputes that the Abrahamic God is inherently simple; if the universe is designed, the designer must be incredibly complex, much as the human brains that design as watches and telescopes are complex. We do not experience spirits as postulated by believers and theologians. According to Blackford, if we viewed the design concept unprejudiced by prior exposure to religious ideas, we would conclude that the existence of the Abrahamic God is highly improbable.  Wilson Pruitt suggested that "(...) Plantinga is not interested in proving the existence of the Christian God but warranting theistic belief. This is not a distinction without a difference." 
Plantinga also supports the notion of God being a "necessary being" in addition to part of a basic belief. In this assertion, "necessary" is defined as "existing in all possible worlds". I.e., no matter what other things we change about hypothetical (or conceptual) alternative realities or futures - these aren't quite the same as the many worlds in quantum mechanics interpretations, but are constructs for the purposes of thought experiments - God must exist in each. The trouble with this is that we can conceive that in one possible world Alvin Plantinga was actually a Muslim, and formulated, through identical reasoning, that Allah is a necessary being that exists in all possible worlds. Which is the main problem with combining quite hardcore philosophy with apologetics.
 Free will and the problem of evil
Plantinga recycles free-will theodicy in an attempt to refute the problem of evil. This still fails to answer the question of evil brought about by non-human causes, such as natural disasters. He justifies this by suggesting that natural disasters could be caused by the free-will of spirits, angels, or devils, which serves to demonstrate how he is really just grasping at straws to justify his beliefs.
 Evolution and intelligent design
Plantinga has at various points voiced support for intelligent design but claims to doubt its scientific validity. He seems to be unaware of the fact that he's arguing in favor of a form of theistic evolution rather than intelligent design. He also argues that a belief in evolution and theism are not mutually exclusive. He's right for once. However, he seems to have backpedaled on this more recently, as he devoted space in his book Where the Conflict Really Lies to defending Michael Behe's ideas about irreducible complexity.
 Evolutionary argument against naturalism (EAAN)
Plantinga claims that evolution, coupled with an atheistic perspective, undermines naturalism. He has called this the "evolutionary argument against naturalism" (EAAN). If there is no God and evolution is correct, that makes the possibility of its own truth, as well as the truth of all other knowledge, either low or negligible. This is because we will be adapted to believe things not because of their truth value but because of their survival value. This appears to reduce to an argument from adverse consequences, as the argument fails to account for the possibility of truth and survival value overlapping, the use of tools to correct for this, and the fact that a whole body of literature in psychology and philosophy has been devoted to dissecting this question.
Moreover, it is not clear how the reference to evolution (in particular, to a scientific account of the origins of the population of modern humans) is significant in the argument, rather than it working at least as well with (to take two very distinct hypotheses) (1) reproduction or development (the origin of the individual) or (2) supernatural (divine or intelligent design) origins of knowledge.
If we, as individual beings with our individual knowledge, are each a result of reproductive and developmental biology, how can we trust what we have learned? There is nothing about reproductive and developmental biology which guarantees that our knowledge is reliable. Just follow through the EAAN making the appropriate substitutions.
If, on the other hand, our knowledge is dependent upon divine (or intelligent design) intervention, how can we trust that?
Plantinga makes a modal argument for mind-body dualism, which is pretty much a repackaged ontological argument. The argument relies on two claims. First, there is the principle of indiscernability of identicals (abbreviated II), which states that if object X and object Y are identical, then X and Y have all the same properties (this may appear to be self-evidently true, but his argument shows that there is a subtle problem with this principle). Second, there is the controversial claim that the conceivability of some scenario implies the possibility of that scenario (abbreviated C-P).
- Science fiction authors can conceive of a great deal that is impossible.
- The god or gods and goddesses of many religions are conceivable. Does that mean all these religions past and present are conceivably true?
Given these claims, Plantiga's argument proceeds as follows: we can imagine (and hence conceive of) a scenario in which our minds exist independently of our bodies. By the C-P principle, this entails that it is possible for our minds to be independent of our bodies. In possible worlds semantics, we would say that there is at least one world in which my mind exists but my body does not. This means that minds and bodies have different modal properties. But the II principle tells us that if objects X and Y are identical then they share all the same properties. Since minds and bodies have different modal properties, it follows (by modus tollens) that minds are not identical to bodies.
The most significant responses to the modal argument fall into two main categories: first, the claim that it is possible for minds to exist independently of bodies has been questioned. This line of argumentation typically proceeds by calling into question the C-P principle or the claim that the fact that I can imagine something entails that I can conceive of it (in the relevant sense). Second, the claim that the II principle applies to modal properties has been attacked; it relies on the principle of necessity of identity, which is widely but not universally accepted.
- While Plantinga claims to have written the book entitled "Where the conflict really lies", it is possible to conceive that he is not the author of the book.
- However, it is not possible that Plantinga is not Plantinga.
- Therefore, Plantinga and the author of the book do not share all properties, and thus Plantinga did not write the book.
As shown above Plantinga's argument can be shown to be manifestly absurd.
- Plantinga's faculty page
- A collection of Plantinga's arguments and responses in philosophical journals archived at Internet Infidels
- Modal argument
- Alvin Plantinga Gives Philosophers a Bad Name, PZ Myers
- Where the Substance Really Isn't, Skeptic magazine
- "Philosopher Sticks Up for God," New York Times, 13 December 2011
- Plantinga's EAAN, Evolving Thoughts
- ↑ Jaco S. Gericke. Fundamentalism on Stilts: A Response to Alvin Platinga's Reformed Epistemology. Verbum et Ecclesia; Vol 30, No 2 (2009).
- ↑ Warrant: The Current Debate, p. 3-5
- ↑ Tyler Wunder – Why Plantinga’s Reformed Epistemology Fails, Common Sense Atheism
- ↑ Warrant: The Current Debate, p. 213
- ↑ Atheism, Pluralism, and Moral Arguments
- ↑ Alvin Plantinga. Is Belief in God Properly Basic? Noûs, Vol. 15, No. 1, 1981 A. P. A. Western Division Meetings (Mar., 1981), pp. 41-51.
- ↑ David W. Felder. Disanalogies in Plantinga's Argument regarding the Rationality of Theism. Journal for the Scientific Study of Religion Vol. 10, No. 3 (Autumn, 1971), pp. 200-207
- ↑ Is a creator god necessarily complex?
- ↑ Atheism, Pluralism, and Moral Arguments
- ↑ Alvin Plantinga. (1980) Does God Have a Nature? Milwaukee, Wis.: Marquette University Press. Reviewed by Alfred J. Freddoso, University of Notre Dame
- ↑ Dean-Peter Baker (ed.). Alvin Plantinga. Cambridge University Press. Reviewed by Edward Wierenga, University of Rochester
- ↑ Alvin Plantinga. Evolution, Shibboleths, and Philosophers. Chronicle of Higher Education, Apr. 11, 2010.
- ↑ Michael Ruse. Alvin Plantinga and Intelligent Design. The Chronicle of Higher Education, Dec. 14, 2011
- ↑ Alvin Plantinga. Naturalism Defeated.
- ↑ Helen de Cruz and Johan de Smedt. Evolved Cognitive Biases and the Epistemic Status of Scientific Beliefs. Philos Stud (2012) 157:411–429
- ↑ Scott Atran. (1990) Cognitive Foundations of Natural History: Towards an Anthropology of Science. Cambridge, UK: Cambridge University Press.