What is Plantinga's "Evolutionary Argument Against Naturalism" (EAAN) in its technical form, and what assumptions does it rely upon?

This argument is among the most precise formulations in Alvin Plantinga's long philosophical career. He first published it in 1993 in "Warrant and Proper Function," then developed it further in "Where the Conflict Really Lies" (2011). The argument is technical and complex, employing probability theory and contemporary epistemology to argue that the conjunction of naturalism and evolution is self-defeating epistemologically. Understanding the precise structure of the argument is necessary for fair evaluation.

Inadequate Responses to Avoid

From some defenders of theism:

"Plantinga proved that evolution is false." This is a fundamental misunderstanding. Plantinga does not attack evolutionary theory, but rather attacks the conjunction of evolution and philosophical naturalism. The argument assumes the truth of evolution and builds upon it. Confusing "critique of evolutionary naturalism" with "critique of evolution" weakens the argument and misrepresents it.

"The argument directly proves God's existence." This exceeds the scope of the argument. EAAN is a negative argument against naturalism, not a positive argument for theism. Even if the argument succeeds, it only establishes that evolutionary naturalism is self-defeating. The move from this to "therefore God exists" requires additional steps that Plantinga has not provided in the argument itself.

From some naturalists:

"Plantinga is just a disguised creationist." This is a cheap accusation. Plantinga is a first-rate analytic philosopher, former president of the American Philosophical Association, and his arguments are discussed in the finest philosophical journals. The argument does not deny evolution but uses it as a premise.

"Evolution guarantees the truth of our beliefs because false beliefs lead to death." This is a misleading oversimplification. This is precisely what the argument challenges: natural selection selects for behavior that leads to survival, not for true beliefs. A false belief can lead to evolutionarily successful behavior.

Why These Responses Are Inadequate

They all fail to understand the precise probabilistic structure of the argument. EAAN is not an argument about evolution or about God's existence, but an epistemological argument about the self-consistency of evolutionary naturalism. Failing to understand this distinction leads to irrelevant discussions.

Technical Structure of the Argument

The argument relies on calculating a conditional probability: P(R|N&E), that is, the probability that our cognitive faculties are reliable (R = Reliable) given the truth of naturalism (N) and evolution (E).

Step One: Analyzing the Relationship Between Beliefs and Behavior

Plantinga distinguishes four possibilities for the relationship between belief content and neurophysiological properties (NP):

1. Epiphenomenalism: Beliefs are byproducts of the brain, they do not affect behavior
2. Semantic epiphenomenalism: The semantic content of beliefs does not affect behavior, only physical properties do
3. Indirect adaptiveness: Beliefs affect behavior but in ways unrelated to their truth
4. Direct adaptiveness: Beliefs affect behavior in ways related to their content

Step Two: Calculating Probabilities

In cases 1-3, natural selection does not select for true beliefs, because they either do not affect behavior, or they affect it in ways unrelated to truth. Therefore P(R|N&E&C₁₋₃) is very low.

In case 4, even if beliefs are influential, Plantinga argues that there are infinitely many false beliefs that would lead to the same adaptive behavior. Example: instead of the true belief "the tiger is dangerous, flee," the false belief "the tiger wants to play with me, and the best way to play with it is to run away from it quickly" could lead to the same successful behavior.

Therefore, even in case 4: P(R|N&E&C₄) ≤ 0.5

Step Three: Final Calculation

Using the law of total probability:
P(R|N&E) = Σᵢ P(R|N&E&Cᵢ) × P(Cᵢ|N&E)

Since each P(R|N&E&Cᵢ) is low or at best moderate, P(R|N&E) is low or inscrutable.

Step Four: The Undercutting Defeater

If P(R|N&E) is low or inscrutable, then a person who believes N&E has a "defeater" for all their beliefs, including N&E itself. This is a special type of defeater: an "undercutting defeater"—it does not directly refute the belief, but undermines confidence in the processes that produced it.

Basic Assumptions of the Argument

1. Content-behavior assumption: There is a possible relationship between belief content and behavior that can be analyzed
2. Probabilistic assumption: Probability calculations can be applied to the reliability of cognitive faculties
3. Strong naturalism assumption: Naturalism means that mental processes are entirely determined by physical-chemical processes
4. Unguided evolution assumption: Evolution is an unguided process that does not aim at truth
5. Epistemological defeater principle: Knowing that the source of your beliefs is unreliable defeats those beliefs

Technical Responses to the Argument

Fodor and Piattelli-Palmarini response (2009): Natural selection does not select for behavior but for mechanisms that produce behavior. Mechanisms that produce true beliefs are simpler and more efficient than mechanisms that produce complex false beliefs. Plantinga responds: This assumes that simplicity and efficiency are connected to truth, an assumption that cannot be justified naturalistically.

William Ramsey response (2002): The distinction between content and neural causation is problematic. In modern naturalism, content is a pattern of neural causation. Plantinga responds: This makes the argument stronger—if content is merely a neural pattern, there is no reason to trust that it corresponds to reality.

Branden Fitelson and Michael Titelbaum response (2015): The argument confuses the reliability of basic cognitive faculties with the reliability of theoretical beliefs. Evolution guarantees the former (seeing the tiger) not the latter (theories about the universe). Plantinga responds: The distinction is artificial—the same faculties used in basic perception are used in theorizing.

Recent Developments (2020-2024)

"Cognitive Naturalism": An attempt to rescue naturalism by developing a more sophisticated evolutionary epistemology. Ruth Millikan and others develop "teleosemantic" theories that link truth to biological function.

"Epistemic Structural Realism": James Ladyman and others argue that what evolution preserves is not the truth of beliefs but the mathematical structure of reality. This might suffice for science without guaranteeing absolute truth.

"Simulation Arguments": Some philosophers argue that EAAN supports the simulation hypothesis (that we are in a computer simulation) as much as it supports theism.

Evaluating the Argument Within the Framework of Rational Preponderance (rajḥān ʿaqlī)

EAAN is a technically strong argument, but it is not decisive. Its success depends on accepting its assumptions, especially about the relationship between content and behavior. The argument shows a real tension in evolutionary naturalism, but does not refute it decisively. Within the framework of cumulative rational preponderance (rajḥān ʿaqlī), EAAN is added as an important element in the balance between theism and naturalism, especially when connected to other arguments (consciousness, fine-tuning, morality).

For Advanced Reading

- Advanced level: Responses to EAAN and critique of responses
- Expert level: EAAN and epistemic Bayesianism
- Plantinga, A. (2011). Where the Conflict Really Lies. Oxford UP.
- Beilby, J. (ed.) (2002). Naturalism Defeated? Cornell UP.
- Fitelson, B. & Sober, E. (1998). "Plantinga's Probability Arguments Against Evolutionary Naturalism," Pacific Phil. Quarterly 79.
- "Formulation: EAAN Technical Structure" page on the website