Plantinga has argued that some people can know that
God exists as a
basic belief, requiring no argument. He developed this argument in two different ways: firstly, in
God and Other Minds (1967), by drawing an equivalence between the
teleological argument and the common sense view that people have of
other minds existing by analogy with their own minds. Plantinga has also developed a more comprehensive epistemological account of the nature of warrant which allows for the existence of God as a basic belief. Plantinga has also argued that there is no logical inconsistency between the
existence of evil and the existence of an all-powerful, all-knowing, wholly good God.
Problem of evil Plantinga proposed a "free-will defense" in a volume edited by
Max Black in 1965, which attempts to refute the
logical problem of evil, the argument that the existence of evil is logically incompatible with the existence of an omnipotent, omniscient, wholly good God. Plantinga's argument (in a truncated form) states that "It is possible that God, even being omnipotent, could not create a world with free creatures who never choose evil. Furthermore, it is possible that God, even being omnibenevolent, would desire to create a world which contains evil if moral goodness requires free moral creatures." However, the argument's handling of
natural evil has been disputed. According to the
Internet Encyclopedia of Philosophy, the argument also "conflicts with important theistic doctrines" such as the notion of a
heaven where free saved souls reside without doing evil, and the idea that God has free will yet is wholly good. Critics thus maintain that, if we take such doctrines to be (as Christians usually have), God could have created free creatures that always do right, contra Plantinga's claim.
J. L. Mackie saw Plantinga's free-will defense as incoherent. Plantinga's well-received book
God, Freedom and Evil, written in 1974, gave his response to what he saw as the incomplete and uncritical view of theism's criticism of
theodicy. Plantinga's contribution stated that when the issue of a comprehensive doctrine of freedom is added to the discussion of the goodness of God and the omnipotence of God then it is not possible to exclude the presence of evil in the world after introducing freedom into the discussion. Plantinga's own summary occurs in his discussion titled "Could God Have Created a World Containing Moral Good but No Moral Evil", where he states his conclusion that, "... the price for creating a world in which they produce moral good is creating one in which they also produce moral evil."
Reformed epistemology What Plantinga calls "Reformed epistemology" holds that belief in God can be rational and justified even without arguments or evidence for the existence of God. More specifically, he argues belief in God is
properly basic, and due to a religious
externalist epistemology, he claims that it could be justified independently of evidence. His externalist epistemology, called "proper functionalism", is a form of
epistemological reliabilism. Plantinga discusses his view of Reformed epistemology and proper functionalism in a three-volume series. In the first book of the trilogy,
Warrant: The Current Debate, Plantinga introduces, analyzes, and criticizes 20th-century developments in analytic epistemology, particularly the works of
Chisholm,
BonJour,
Alston,
Goldman, and others. In the book, Plantinga argues specifically that the theories of what he calls "warrant"—what many others have called
justification (Plantinga draws out a difference: justification is a property of a person holding a belief while warrant is a property of a belief)—put forth by these epistemologists have systematically failed to capture in full what is required for knowledge. In the second book,
Warrant and Proper Function, he introduces the notion of warrant as an alternative to justification and discusses topics like self-knowledge, memories, perception, and probability. Plantinga's "proper function" account argues that as a necessary condition of having warrant, one's "belief-forming and belief-maintaining apparatus of powers" are functioning properly—"working the way it ought to work". Plantinga explains his argument for proper function with reference to a "design plan", as well as an environment in which one's cognitive equipment is optimal for use. Plantinga asserts that the design plan does not require a designer: "it is perhaps possible that evolution (undirected by God or anyone else) has somehow furnished us with our design plans", but the paradigm case of a design plan is like a technological product designed by a human being (like a radio or a wheel). Ultimately, Plantinga argues that epistemological
naturalism—i.e.
epistemology that holds that warrant is dependent on natural faculties—is best supported by supernaturalist metaphysics—in this case, the belief in a
creator God or designer who has laid out a design plan that includes cognitive faculties conducive to attaining knowledge. According to Plantinga, a belief, B, is warranted if: (1) the cognitive faculties involved in the production of B are functioning properly...; (2) your cognitive environment is sufficiently similar to the one for which your cognitive faculties are designed; (3) ... the design plan governing the production of the belief in question involves, as purpose or function, the production of true beliefs...; and (4) the design plan is a good one: that is, there is a high statistical or objective probability that a belief produced in accordance with the relevant segment of the design plan in that sort of environment is true. Plantinga seeks to defend this view of proper function against alternative views of proper function proposed by other philosophers which he groups together as "naturalistic", including the "functional generalization" view of
John Pollock, the evolutionary/etiological account provided by
Ruth Millikan, and a dispositional view held by
John Bigelow and Robert Pargetter. Plantinga also discusses his
evolutionary argument against naturalism in the later chapters of
Warrant and Proper Function. In 2000, the third book of the trilogy,
Warranted Christian Belief, was published. In this volume, Plantinga's warrant theory is the basis for his theological end: providing a philosophical basis for Christian belief, an argument for why Christian theistic belief can enjoy warrant. In the book, he develops two models for such beliefs, the "A/C" (
Aquinas/
Calvin) model, and the "Extended A/C" model. The former attempts to show that a belief in God can be justified, warranted and rational, while the Extended model tries to show that specifically Christian theological beliefs including the
Trinity, the
Incarnation, the
resurrection of Christ, the
atonement,
salvation. etc. Under this model, Christians are justified in their beliefs because of the work of the
Holy Spirit in bringing those beliefs about in the believer. James Beilby has argued that the purpose of Plantinga's
Warrant trilogy, and specifically of his
Warranted Christian Belief, is firstly to make a form of argument against religion impossible—namely, the argument that whether or not Christianity is true, it is irrational—so "the skeptic would have to shoulder the formidable task of demonstrating the falsity of Christian belief" rather than simply dismiss it as irrational. In addition, Plantinga is attempting to provide a philosophical explanation of how Christians should think about their own Christian belief.
Modal ontological argument Plantinga has expressed a
modal logic version of the ontological argument in which he uses
modal logic to develop, in a more rigorous and formal way,
Norman Malcolm's and
Charles Hartshorne's modal
ontological arguments. Plantinga criticized Malcolm's and Hartshorne's arguments, and offered an alternative. He argued that, if Malcolm does prove the necessary existence of the greatest possible being, it follows that there is a being which exists in all worlds whose greatness in
some worlds is not surpassed. It does not, he argued, demonstrate that such a being has unsurpassed greatness in this world. In an attempt to resolve this problem, Plantinga differentiated between "greatness" and "excellence". A being's excellence in a particular world depends only on its properties in that world; a being's greatness depends on its properties in all worlds. Therefore, the greatest possible being must have maximal excellence in every possible world. Plantinga then restated Malcolm's argument, using the concept of "maximal greatness". He argued that it is possible for a being with maximal greatness to exist, so a being with maximal greatness exists in a possible world. If this is the case, then a being with maximal greatness exists in every world, and therefore in this world. A version of his argument is as follows: • A being has
maximal excellence in a given possible world
W if and only if it is omnipotent, omniscient and wholly good in
W; and • A being has
maximal greatness if it has maximal excellence in every possible world. • It is possible that there is a being that has maximal greatness. (Premise) • Therefore, possibly, it is necessarily true that an omniscient, omnipotent, and perfectly good being exists. • Therefore, (by axiom S5) it is necessarily true that an omniscient, omnipotent and perfectly good being exists. • Therefore, an omniscient, omnipotent and perfectly good being exists. Plantinga argued that, although the first premise is not rationally established, it is not contrary to reason.
Michael Martin argued that, if certain components of perfection are contradictory, such as omnipotence and omniscience, then the first premise is contrary to reason. Martin also proposed parodies of the argument, suggesting that the existence of anything can be demonstrated with Plantinga's argument, provided it is defined as perfect or special in every possible world. Another Christian philosopher,
William Lane Craig, characterizes Plantinga's argument in a slightly different way: • It is possible that a maximally great being exists. • If it is possible that a maximally great being exists, then a maximally great being exists in some possible world. • If a maximally great being exists in some possible world, then it exists in every possible world. • If a maximally great being exists in every possible world, then it exists in the actual world. • If a maximally great being exists in the actual world, then a maximally great being exists. • Therefore, a maximally great being exists. According to Craig, premises (2)–(5) are relatively uncontroversial among philosophers, but "the epistemic entertainability of premise (1) (or its denial) does not guarantee its metaphysical possibility." Furthermore,
Richard M. Gale argued that premise three, the "possibility premise",
begs the question. He stated that one only has the epistemic right to accept the premise if one understands the nested
modal operators, and that if one understands them within the system S5—without which the argument fails—then one understands that "possibly necessarily" is in essence the same as "necessarily". Thus the premise begs the question because the conclusion is embedded within it. On S5 systems in general, James Garson writes that "the words 'necessarily' and 'possibly', have many different uses. So the acceptability of axioms for modal logic depends on which of these uses we have in mind."
Evolutionary argument against naturalism In Plantinga's
evolutionary argument against naturalism, he argues that if evolution is true, it undermines
naturalism. His basic argument is that if evolution and naturalism are both true, human cognitive faculties evolved to produce beliefs that have survival value (maximizing one's success at the four Fs: "feeding, fleeing, fighting, and reproducing"), not necessarily to produce beliefs that are true. Thus, since human cognitive faculties are tuned to survival rather than truth in the naturalism-evolution model, there is reason to doubt the veracity of the products of those same faculties, including naturalism and evolution themselves. On the other hand, if God created man "
in his image" by way of an evolutionary process (or any other means), then Plantinga argues our faculties would probably be reliable. The argument does not assume any necessary correlation (or uncorrelation) between true beliefs and survival. Making the contrary assumption—that there is, in fact, a relatively strong correlation between truth and survival—if human belief-forming apparatus evolved giving a survival advantage, then it ought to yield truth since true beliefs confer a survival advantage. Plantinga counters that, while there may be overlap between true beliefs and beliefs that contribute to survival, the two kinds of beliefs are not the same, and he gives the following example with a man named Paul: The argument has received favorable notice from
Thomas Nagel and
William Lane Craig, but has also
been criticized as seriously flawed, for example, by
Elliott Sober.
View on naturalism and evolution Even though Plantinga believes that God could have used Darwinian processes to create the world, he stands firm against philosophical
naturalism. He said in an interview on the
relationship between science and religion that: Religion and science share more common ground than you might think, though science can't prove, it presupposes that there has been a past for example, science does not cover the whole of the knowledge enterprise. Plantinga participated in groups that support the
Intelligent Design Movement, and was a member of the "Ad Hoc Origins Committee" that supported
Philip E. Johnson's 1991 book
Darwin on Trial, he also provided a back-cover endorsement of Johnson's book: "Shows how Darwinian evolution has become an idol." He was a Fellow of the (now defunct) pro-intelligent design
International Society for Complexity, Information, and Design, and has presented at a number of intelligent design conferences. In a March 2010 article in
The Chronicle of Higher Education, philosopher of science
Michael Ruse labeled Plantinga as an "open enthusiast of intelligent design". In a letter to the editor, Plantinga made the following response: Like any Christian (and indeed any theist), I believe that the world has been created by God, and hence "intelligently designed". The hallmark of intelligent design, however, is the claim that this can be shown scientifically; I'm dubious about that. ...As far as I can see, God certainly could have used Darwinian processes to create the living world and direct it as he wanted to go; hence evolution as such does not imply that there is no direction in the history of life. What does have that implication is not evolutionary theory itself, but
unguided evolution, the idea that neither God nor any other person has taken a hand in guiding, directing or orchestrating the course of evolution. But the scientific theory of evolution, sensibly enough, says nothing one way or the other about divine guidance. It doesn't say that evolution is divinely guided; it also doesn't say that it isn't. Like almost any theist, I reject unguided evolution; but the contemporary scientific theory of evolution just as such—apart from philosophical or theological add-ons—doesn't say that evolution is unguided. Like science in general, it makes no pronouncements on the existence or activity of God. The attitude that he proposes and elaborates upon in
Where the Conflict Really Lies: Science, Religion and Naturalism is that there is no tension between religion and science, that the two go hand in hand, and that the actual conflict lies between naturalism and science. == Selected works ==