Argument from Incredulity: When "I Can't Imagine It" Becomes Proof

In 1802, the theologian William Paley opened his Natural Theology with a famous thought experiment. Crossing a heath, he comes across a watch lying on the ground. Unlike a stone, the watch's parts are so intricately fitted together for a purpose that he could not conceive of them having come about by accident. The watch must have had a maker. And if the watch is complex beyond chance, how much more so the human eye, the human heart, the workings of the living world? The argument is elegant. It is also a fallacy — and one of the most enduring in the history of human thought.

What Is the Argument from Incredulity?

The argument from incredulity (sometimes called the appeal to incredulity or personal incredulity fallacy) occurs when someone treats their own inability to imagine how something is true as evidence that it cannot be true — or their inability to imagine how something is false as evidence that it must be true. The logical form is:

1. I cannot conceive how X could be the case (or how X could not be the case).
2. Therefore X is not the case (or must be the case).

The fallacy is in the inference. A failure of personal imagination tells us something about the limits of one person's understanding. It tells us nothing about the actual state of the world. The history of science, mathematics, and philosophy is a catalogue of ideas that were incomprehensible to virtually everyone until they were understood — and then became obvious in retrospect. The universe does not calibrate its workings to human intuition.

Paley's Watch and Evolutionary Biology

Paley's watchmaker argument is the most famous deployment of argument from incredulity in Western intellectual history. His core claim was that the complexity of biological organisms is so improbable as to be inconceivable without a designer. This argument was widely persuasive until Charles Darwin provided, in 1859, a mechanism — natural selection — by which precisely this kind of complexity could arise through purely natural processes.

Darwin's achievement was not merely empirical but conceptual: he provided a mechanism that made the complexity of life imaginable without design. Once the mechanism was specified, the incredulity dissolved. This is the standard story of argument from incredulity: the limits of understanding at a given moment in time are mistaken for limits on what is possible in principle.

Richard Dawkins, in his 1986 book The Blind Watchmaker, addressed this directly. "Argument from personal incredulity," he wrote, "is a deeply fallacious argument. It doesn't matter how improbable something seems to an untrained human mind. What matters is whether there is a coherent naturalistic mechanism. And in the case of evolution, there demonstrably is." The eye — so often cited as an impossibly complex organ that no random process could produce — has in fact evolved independently at least forty times in the history of life, through documented, understood incremental stages.

Intelligent Design: The Same Argument Refined

The intelligent design movement, which emerged prominently in the 1990s and reached a legal climax at the 2005 Kitzmiller v. Dover trial, reformulated Paley's argument in the language of information theory and molecular biology. The concept of "irreducible complexity," developed by biochemist Michael Behe, argued that certain biochemical systems — the bacterial flagellum, the blood-clotting cascade — were so intricately interdependent that removing any single part would destroy their function, making their gradual evolution inconceivable.

Critics — and the federal court — found the argument familiar. The fact that Behe could not imagine an evolutionary pathway for the flagellum did not constitute evidence that no such pathway existed. Subsequent biological research identified precursor structures and plausible evolutionary sequences for every system Behe had claimed was irreducibly complex. The argument from incredulity had been dressed in biochemical vocabulary, but its structure was unchanged from 1802.

Quantum Mechanics and the Intuition Barrier

Physics offers a particularly instructive case. Quantum mechanics is not merely counterintuitive — it violates the deepest assumptions of ordinary experience. Particles exist in superposition until observed. Entangled particles influence each other instantaneously across arbitrary distances. Objects have definite positions only when measured. The physicist Niels Bohr reportedly said that anyone not shocked by quantum theory hasn't understood it.

The argument from incredulity response to quantum mechanics — "this cannot be true, because I cannot conceive how it could be" — has been offered by serious physicists, including Albert Einstein, who spent decades trying to demonstrate that quantum mechanics must be incomplete because its implications were too strange to accept. ("God does not play dice.") The experimental record has been unkind to this intuition. Bell's theorem, tested in increasingly rigorous experiments since the 1970s, confirms that quantum entanglement is real and that classical intuitions about locality are simply wrong about how the universe operates.

The universe is under no obligation to be imaginable. What we find incredible tells us about the limits of our evolved intuitions — intuitions shaped for navigating a medium-sized world at medium speeds. They are not a reliable guide to the behaviour of particles, cosmological scales, or evolutionary timescales.

Economic Models and Social Complexity

The argument from incredulity appears outside science as well, often in debates about complex social and economic systems. "I cannot imagine how spontaneous market processes could coordinate the production and distribution of billions of goods — so they couldn't." "I cannot conceive of how a system without central planning could allocate resources efficiently — so it can't." "I cannot understand how a process without a guiding intention could produce the structures of language — so language must have been designed."

Each of these incredulities has driven significant intellectual and political error. Market coordination, language evolution, and self-organising systems are all well-understood phenomena that are genuinely counterintuitive — they require sustained intellectual effort to grasp. The inability to immediately understand them is evidence of their complexity, not of their impossibility.

The "God of the Gaps" Connection

The argument from incredulity is the engine of God of the Gaps reasoning — the pattern of inserting divine (or magical, or conspiratorial) causation wherever natural explanation seems insufficient or unavailable. "We don't know how life began — therefore God." "Science can't explain consciousness — therefore the soul." "How could this coincidence happen by chance — therefore it was arranged."

Each gap in understanding is treated as positive evidence for an alternative — when in fact it is only evidence of a gap in understanding. Gaps close. Scientific fields routinely absorb problems that seemed intractable and explain them through mechanisms that were initially inconceivable. The history of the "God of the Gaps" is a history of retreating perimeters.

This does not mean that all gaps will close or that all things are explicable in principle. It means that the current inability to explain X is weak evidence against any particular explanation, and that using personal incredulity as a proxy for impossibility is repeatedly, historically shown to be unreliable.

Why the Fallacy Persists

The argument from incredulity is psychologically powerful for several reasons:

• Imagination feels like understanding. If we can vividly picture how something works, we tend to find it credible. If we can't picture it, it feels implausible. This is a heuristic, not a method.
• Complexity is intimidating. Evolution, quantum mechanics, and macroeconomics all require substantial background knowledge to understand. The failure to understand them is easy to mistake for a failure in the theories themselves.
• Personal experience is the default reference frame. Human intuitions are calibrated to everyday scales and speeds. Applying them to geological timescales, quantum scales, or evolutionary biology consistently generates false conclusions.
• Alternative explanations are satisfying. If the natural explanation seems inconceivable, an intentional explanation (a designer, a conspirator, a plan) fills the psychological gap with something comprehensible.

Distinguishing Incredulity from Genuine Scepticism

Not all expressions of disbelief are arguments from incredulity. Genuine scientific scepticism asks: what is the evidence? What are the mechanisms? What predictions does the theory make, and have they been tested? This is different from: I cannot imagine how this could be true, therefore it isn't.

The test is whether the "I can't imagine" is followed by a request for explanation (genuine inquiry) or by a conclusion about the world (fallacious inference). A student who cannot yet visualise how natural selection produces eyes and asks for a more detailed mechanism is doing science. One who concludes from their current inability to visualise it that it could not have happened is deploying the fallacy.

A related distinction: the Burden of Proof pattern addresses cases where incredulity is used to demand evidence from the other side rather than claiming proof of falsehood. "I can't see how evolution works, so you need to prove it" is not quite an argument from incredulity — it is a burden-shifting move. But the two are often found together.

Related Patterns

• Argument from Ignorance — "it hasn't been proven true, so it must be false" (and vice versa); close relative, often confused
• Burden of Proof — misassigning the responsibility to demonstrate a claim
• Dunning-Kruger Effect — limited understanding creating unwarranted confidence in that limit
• False Cause — inferring causation from inability to imagine an alternative causal story
• Appeal to Nature — a related form, where incomprehension of natural complexity invites a design inference

Sources & Further Reading

• Paley, William. Natural Theology. 1802.
• Darwin, Charles. On the Origin of Species. John Murray, 1859.
• Dawkins, Richard. The Blind Watchmaker. Norton, 1986.
• Behe, Michael. Darwin's Black Box. Free Press, 1996. (The primary intelligent design source; for the refutation, see Kitzmiller v. Dover ruling.)
• Carroll, Sean B. The Making of the Fittest: DNA and the Ultimate Forensic Record of Evolution. Norton, 2006.
• Internet Encyclopedia of Philosophy: Informal Fallacies
• Wikipedia: Argument from Ignorance (overlapping analysis)
• RationalWiki: Argument from Incredulity