The Evolutionary Argument Against Naturalism is Plantinga’s central argument for Naturalism’s Internal Contradiction and the deep conflict between science and naturalism. The argument asserts that if both naturalism and evolution are true, then the probability that our cognitive faculties are reliable (i.e., that they produce mostly true beliefs) is low or inscrutable. This is because natural selection favors adaptive behaviors that promote survival and reproduction. A creature’s belief content is a byproduct of its neurophysiology (NP properties), but it is the NP properties that cause behavior, regardless of whether the associated belief is true. As Patricia Churchland notes, from an evolutionary perspective, “Truth, whatever that is, definitely takes the hindmost” (315). This point was even articulated by Charles Darwin himself, who expressed the “horrid doubt” of whether human convictions, having developed from lower animals, were at all trustworthy.

Plantinga argues that if the probability of having reliable faculties is low, then a person who accepts both naturalism and evolution has a powerful reason to doubt the reliability of their own cognitive faculties. This doubt functions as a defeater for all their beliefs, including the belief in naturalism and evolution itself. The naturalist is thus caught in a self-defeating loop: Accepting the premises of naturalistic evolution undermines the very rationality required to trust that conclusion. Therefore, Plantinga concludes, one cannot rationally accept both naturalism and evolution, revealing a fundamental incompatibility between the naturalistic worldview and a core pillar of modern science.

The Fine-Tuning Argument is a contemporary argument for theism based on the scientific discovery that many fundamental physical constants of the universe must fall within an extraordinarily narrow range of values for life to be possible. Had the force of gravity, the cosmological constant, or the strong and weak nuclear forces been even slightly different, the universe would not have been able to support complex, intelligent life. This extreme improbability of a life-permitting universe, Plantinga argues, is surprising on the hypothesis that the universe arose by chance, but unsurprising on the hypothesis that it was created by a purposeful God.

While this argument faces several objections, Plantinga suggests they are not decisive. The anthropic principle, which states that we could only observe a universe capable of supporting us, explains why we do not observe a non-tuned universe but fails to explain why a tuned one exists in the first place. The “multiverse” or “many-worlds” hypothesis, which posits an enormous number of universes with varying constants, might explain why some universe is fine-tuned, but it does not make it any more probable that this particular universe would be the one. Ultimately, Plantinga concludes that the FTA offers modest support for God’s existence, demonstrating a concord between discoveries in physics and theistic belief.

The Laplacean Picture describes a view of the universe, emerging from an interpretation of classical physics, as a deterministic and causally closed system. It is famously captured by the thought experiment of Pierre Laplace, who imagined a vast intellect, or demon, that could, if given the precise state of the universe at one moment, predict all future states and retrodict all past ones. This mind “would embrace […] the movements of the greatest bodies of the universe and those of the lightest atom” (84), leaving nothing uncertain. In this view, every physical event is necessitated by prior physical events and the inviolable laws of nature, leaving no room for any outside causal influence.

Plantinga identifies this picture as a key source of alleged conflict between science and religion, particularly concerning divine action and free will. If the universe is a closed causal system, then any special divine act, such as a miracle, would be impossible. However, he argues that the Laplacean Picture is not a conclusion of classical science itself but a metaphysical or theological add-on. Newtonian laws, for instance, were formulated for closed systems, but they do not assert that the universe is a closed system. Furthermore, the advent of quantum mechanics, with its inherent indeterminism, has scientifically superseded the deterministic certainty of the Laplacean worldview, showing it to be an outdated foundation for rejecting divine action.

Methodological Naturalism is the procedural rule or constraint that science should be practiced without reference to supernatural beings or causes. It dictates that scientific theories, evidence, and explanations should rely solely on natural phenomena. Plantinga notes that this is a widely held convention, with proponents like Eugenie Scott arguing that “Science neither denies or opposes the supernatural, but ignores the supernatural for methodological reasons” (170). A clear example of its application was the 2005 Dover trial, where Intelligent Design was ruled to be non-scientific precisely because it “violates the centuries-old ground rules of science by invoking and permitting supernatural causation” (171).

Plantinga distinguishes between a “weak” form of MN, which merely excludes theistic premises from the scientific evidence base, and a “strong” form, which actively includes atheistic premises (e.g., that miracles do not happen). In either case, he argues that MN creates a scientific evidence base that is significantly narrower than a Christian one. This difference explains why some scientific conclusions, particularly in fields like evolutionary psychology and historical biblical criticism, may conflict with Christian belief. However, Plantinga contends that this conflict is “superficial” because the scientific conclusions are founded on a deliberately restricted evidence base. They do not, therefore, automatically provide a defeater for Christian beliefs, which are held on the basis of a fuller set of evidence that includes faith and revelation.