A new study suggests that people who are strongly drawn to conspiracy theories may be more willing to believe mutually incompatible explanations at the same time—a pattern the researchers describe as a departure from Bayesian rationality. The finding offers a new way to study conspiratorial thinking, not simply by asking whether people believe particular claims, but by examining whether the strength of their beliefs is logically consistent. In a series of analyses involving more than 9,000 participants, researchers found that incoherent belief was closely associated with conspiracism, especially when incompatible explanations challenged official or conventional accounts of events.
The study, led by Alessandro Miani of the University of Bristol School of Psychological Science, applies a mathematical framework from probability theory to a long-running question in psychology: do people who endorse one conspiracy theory also tend to accept other theories that contradict it? Previous research has often treated belief as a yes-or-no response. A participant might be classified as believing or disbelieving a statement based on whether they agree with it. But real-world belief is rarely so absolute. People can regard a claim as possible, likely, highly likely or almost certain. The researchers therefore treated survey responses as subjective probabilities rather than as simple categories.
This approach is based on Bayesian reasoning, a framework used in science, statistics and artificial intelligence to update beliefs in response to evidence. Under the framework, a person can rationally assign a 50 percent probability to each of two mutually exclusive possibilities. That would represent uncertainty, not contradiction. However, assigning a 90 percent probability to both possibilities creates a mathematical problem. If the alternatives cannot both be true, their probabilities cannot add up to more than 100 percent. A person who assigns high confidence to both is expressing what the researchers call an incoherent set of beliefs. The issue is not that someone entertains several possibilities, but that the strength of their beliefs violates the rules governing probabilities.
Miani and his colleagues first reanalyzed data from eight previously conducted studies involving 8,590 participants. These datasets included measures of conspiracy belief and responses to pairs of claims that could not both be true. The researchers converted agreement ratings into estimated probabilities and then calculated whether participants’ combined judgments exceeded the maximum probability allowed by the logical relationship between the statements. The pattern was striking: the estimated likelihood that a participant held incoherent beliefs increased from approximately 3 percent among the weakest conspiracy believers to about 91 percent among the strongest. The result does not mean that every person with strong conspiratorial views reasons incoherently, but it indicates a powerful statistical relationship between conspiracy mentality and violations of probabilistic consistency.
The researchers then tested the idea in a new preregistered online study involving 469 Americans. Participants read 16 fictional scenarios designed to avoid the influence of prior knowledge or political controversy. One scenario described an eight-year-old girl, the daughter of a European Parliament member, who disappeared for three days. Participants were asked to judge how probable it was that she had been secretly held by her father as part of a scheme to misuse public funds. They also rated the probability that she had escaped from an environment where she was secretly forced into child labor. The two explanations were incompatible, yet both were designed to challenge an official or socially expected interpretation of the disappearance.
Participants with higher scores on a standardized five-item measure of conspiracy mentality were more likely to assign high probabilities to both explanations. Their responses suggested that they were not merely uncertain about what had happened. Instead, they were more likely to endorse two different conspiratorial narratives strongly enough that their probabilities exceeded 100 percent when added together. The finding is important because the two explanations did not simply represent different versions of the same story. They required mutually exclusive accounts of the girl’s circumstances, yet both appeared attractive to people with stronger general tendencies toward conspiratorial thinking.
The pattern changed when the incompatible explanations were ordinary accidents rather than conspiracies. In another scenario, participants considered two possibilities that could not both be true: the girl had fallen from a nearby cliff, or she had been caught in an avalanche. Conspiracy mentality scores did not predict the tendency to assign high probabilities to both mundane explanations. This suggests that the relationship between conspiracism and incoherence is not a general inability to understand that alternatives can conflict. Instead, the effect appears to depend partly on the kind of explanation being evaluated. People inclined toward conspiracy theories may be especially vulnerable to endorsing incompatible accounts when those accounts share a common narrative structure—namely, the idea that hidden forces, wrongdoing or suppressed information lie behind an event.
The researchers also examined pairs in which one statement was the strict negation of the other. For example, if one claim says that a particular event happened, its negation says that it did not happen. In such cases, the two probabilities must sum to exactly 100 percent. A person who assigns a 70 percent probability that a statement is true should, under classical probability rules, assign 30 percent to its negation. Conspiracy mentality predicted incoherence in these strict-negation judgments as well, even when the content was not conspiratorial. This result points to a second component of the phenomenon: a broader reduction in logical monitoring that may cause people to overlook the relationship between a claim and its direct opposite.
Together, the findings suggest that incoherence in conspiracism may arise through at least two related pathways. The first is general and concerns the ability or motivation to monitor logical relationships between statements. It appears when people evaluate direct contradictions, regardless of whether the subject matter involves a conspiracy. The second is content-specific. It emerges when people assign strong confidence to separate conspiratorial explanations that are incompatible with one another. In this case, the attraction may come from a worldview that prioritizes hidden agency, institutional deception and counter-narratives over ordinary explanations, allowing several competing stories to feel compelling at the same time.
The study does not establish that incoherent reasoning causes conspiracy beliefs, and it does not suggest that all conspiracy theories are false simply because they are conspiratorial. Real conspiracies can occur, and people may reasonably remain uncertain when evidence is incomplete. The researchers’ method instead focuses on the consistency of confidence assigned to claims that cannot simultaneously be true. Survey-based probability estimates also depend on how participants interpret rating scales, and the fictional scenarios cannot reproduce the full emotional and social context of real-world controversies. Nevertheless, by replacing binary belief categories with quantitative measures of subjective probability, the work provides a sharper tool for investigating how conspiracy beliefs are structured. Its central message is likely to attract broad attention: the issue may not be that conspiratorial thinkers believe too little, but that they can sometimes believe too much of several incompatible stories at once.
Subject of Research: Psychological science, conspiratorial thinking, Bayesian reasoning, belief incoherence
Article Title: Still very much dead and alive: Incoherence in conspiracism as a departure from Bayesian rationality
News Publication Date: 18-Aug-2026
References: PNAS Nexus
Keywords: Conspiracy theories, conspiracism, incoherent beliefs, Bayesian rationality, probability judgments, logical inconsistency, psychology, belief formation, cognitive science
