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Intentionality bias, which is known as intention bias for short, is a bias that makes people believe that all human behavior is intentional and that unconscious and/or accidental behavior is less likely behavior. This cognitive bias can happen even if the evidence against the assumption is presented to the person. This tendency has extensive ramifications for societal dynamics, interpersonal relationships, as well as conflict resolution. Intentionality bias may result in misjudgment of people’s behavior, misunderstanding as well as miscommunication. This tendency may contribute to unfavorable prejudices and stereotypes, escalate conflicts and stigmatize people.^[1]

Forming judgements about intentions is a cornerstone of human social functioning, as they influence how we perceive, respond to, and predict other people’s behaviour.^[2] A series of psychological studies demonstrated that adults implicitly and automatically gravitate towards intentional explanations of actions, a phenomenon termed ‘intentionality bias’.^{[3] [4]} Interestingly, this tendency was also documented in children when they believed that natural events were created intentionally even by a non-human agent, and they tended to attribute intentions to artifacts.^{[5] [6]}

In her seminal work, Rosset (2008) proposed a paradigm for examining intentionality bias, which later laid the methodological foundation of this research area. In Rosset’s experiments, participants were presented with blocks of sentences, each of which contained several test and control sentences. While test sentences described behaviours with ambiguous intentions, control sentences described either unambiguously deliberate or unambiguously accidental actions. These sentences were shown consecutively and participants judged if each action was done “on purpose” or “by accident”.

However, the author admitted a fundamental flaw in her paradigm which may undermine the internal validity of findings: written sentences may reflect a linguistic bias rather than intentionality bias, as different wording may imply different levels of intentions.^[3]

Moore and Pope (2014) built on this limitation and developed a novel procedure that utilises visual stimuli to investigate intentionality bias. In their study, participants were presented with short video clips depicting ambiguous movements, then verbally reported whether they believed each movement was performed intentionally or accidentally. This refinement thus allowed researchers to accurately capture intentionality bias.^[4]

One explanation for intentionality bias is the dual-process model of intention attribution. Rosset (2008) suggested that intentional judgements are made automatically and nonconsciously due to intentionality bias, thus serving as a cognitive default. This involuntary response can be overridden or inhibited by higher levels of processing, which develop with age and knowledge of alternative causes and social norms. Moreover, participants were more likely to attribute intentions to prototypically accidental actions, and they recalled more unintentional sentences than intentional ones, indicating that making accidental judgements is cognitively expensive and requires more processing.^[3]

The importance of higher cognitive processes in overriding intentionality bias is further highlighted in a study of anger and its impact on intentional inferences. Angry individuals were found to make more intentional judgements compared to non-angry participants, possibly due to their greater reliance on superficial cognitive processing.^[7]

As an extension from the dual-process model, impaired inhibitory control was put forward as an underlying mechanism of intentionality bias. Research revealed that schizophrenic patients showed a significant tendency to over-attribute intentions to actions compared to healthy participants, thus suggesting a link between inhibitory processes and intentionality bias.^[8] Furthermore, alcohol has been shown to reduce inhibitory control, and intoxicated individuals were more likely to interpret actions as deliberate compared to sober people.^[9][10] Moreover, time pressure was shown to reduce self-regulatory abilities, and under time constraints, participants made more intentional judgements since they may not have accessed resources to inhibit automatic responses.^[3][11]

Another possible explanation for intentionality bias stems from the error management theory of cognitive biases, which states that cognitive biases emerge when the costs of false-positive and false-negative errors are unbalanced.^[12] According to Moore and Pope (2014), it may be more beneficial to attribute intentionality to others’ behaviour, because a false-positive error (i.e. believing an action is intentional when it is accidental) is less detrimental than a false-negative error (i.e. believing an action is accidental when it is intentional). Consequently, intentionality bias prompts individuals to be alert to the involvement of other agents who may be a threat, making it an adaptive cognitive response.^[4]

The magnitude of intentionality bias may vary individually. Findings suggested that individuals with higher cognitive empathy (i.e. the ability to understand people’s emotions) and better perspective-taking skills were more prone to making intentional judgements. Conversely, affective empathy (i.e. the ability to vicariously experience people’s emotions) was not a reliable predictor of intention inferences. This suggested that cognitively empathetic individuals may have an overly sensitive system of intention attribution.^[13]

Research also revealed that the extent of intentionality bias was associated with individual differences in schizotypy (i.e. schizophrenia-like symptoms found in healthy people). Participants who scored higher on the schizotypy rating scales tended to exhibit stronger bias compared to those who scored lower.^[4] Additionally, social actions were more likely to be judged as intentional compared to non-social events among individuals with schizophrenia-like traits, thus strengthening the link between intentionality bias and deficits in inhibitory control.^[14]

Research into intentionality bias suggested that humans are inclined towards intentional judgements, which had significant implications for the understanding of everyday situations.^[15] For instance, intentionality bias was associated with aggressive behaviour, and aggressive children were more likely to attribute hostile intentions to a peer.^[16] Moreover, intentional inferences are often accompanied by accountability attribution, and individuals were more motivated to blame intentional harm-doers.^{[17] [18]}

On a societal level, judgements of intentionality are especially crucial in law enforcement, where the decision of whether someone is guilty or innocent is contingent on how intentional their actions were. For example, when a killing is shown to be intentional, a defendant may be accused of murder rather than manslaughter and receive more severe punishment. Therefore, intentionality bias highlights the importance of the rule that assumes people are innocent by default until proven otherwise.^[3]

Furthermore, a link between the endorsement of conspiracy theories and intentionality bias has been discovered. Brotherton and French (2015) showed that individuals with stronger bias towards intentional explanations of behaviour were more likely to find conspiracy theories plausible.^[19] Thus, investigations into intentionality bias may illuminate the spread and mechanism of conspiracy theories.

However, there is some counter-evidence that challenges the effect of the intentionality bias. A replication study failed to reproduce the results of Rosset (2008), and findings revealed that participants were not more likely to make intentional judgements in a speeded compared to an unspeeded condition. Moreover, participants made unintentional judgements faster and more consistently than intentional ones, which contradicted the predictions of intentionality bias.^{[3] [20]}

Furthermore, Rosset’s dual-process model of intention attribution may be oversimplistic or incomplete. Eisenkoeck et al. (2024) found that contrary to Rosset’s predictions that higher cognitive load would increase intentional judgements due to insufficient resources inhibiting automatic responses, participants with increased working memory cognitive load were not more susceptible to intentionality bias.^[21] This evidence suggests that making intentional inferences may be more complex than a simple two-process model.