Swearing An Oath To God More Likely to Get You Acquitted in Court, Study Finds

Research suggests jurors who take religious oaths in court are more likely to be prejudiced against defendants who opt for a secular alternative. Is it time to change this type of legal practice?

Russell is a Science Writer with IFLScience and has a PhD in the History of Science, Medicine and Technology

Dr. Russell Moul

Russell is a Science Writer with IFLScience and has a PhD in the History of Science, Medicine and Technology.

Science Writer

A court gavel rests on a stand with two books on law and a pair of scales in the background.

A new study suggests potentially harmful bias in the legal system. Image credit: Africa Studio/

Researchers have found that defendants who refuse to swear an oath to God are more likely to be found guilty by jurors with religious beliefs. The study asks whether it is time for this legal ritual to be updated.

When giving evidence in courts in countries like Britain, Ireland, Australia, and the USA, a witness will be asked whether they wish to take an oath or to affirm that their statements are true. The former represents a religious commitment to be honest while the latter, an affirmation, is a secular version of this same pledge – it just doesn’t mention the Almighty or any other supernatural entity. 


In both instances, the nature of the declaration is meant to demonstrate a public commitment to truthfulness, based on values that are intended to be treated equally, at least in terms of the law. However, research led by a team from Royal Holloway, University of London, suggests this is not always the case. 

The idea that atheists and non-religious individuals are somehow morally suspicious is common across the world and is deeply ingrained in various societies. In Britain, 20 percent of a surveyed population explicitly agreed that “morality is impossible without the belief in God”; the number was even higher in the US, with 44 percent of Americans expressing agreement. According to a cross-national study published in 2017, distrust in atheists was so pervasive that it even extended to other non-believers. The study found that the overwhelming influence of religion on moral prejudice entrenched anti-atheist ideas, even among non-believers in secular societies. 

The significance of this moral suspicion against non-believers has implications in legal practice, as it could lead to bias, despite claims that such systems operate dispassionately. This is what the team from Royal Holloway sought to investigate. They did so by conducting research in stages. In the first two stages, the team found that people associated religious oaths with convincing testimonies. They also found that religious individuals were biased against defendants who chose a secular pledge. 

“The results of our first two studies”, the authors explain “indicate that court witnesses who swear an oath are, on average, much more religious than those who choose to affirm; that witnesses who swear are perceived as much more religious than those who affirm; that people associate choice of the oath with credible testimony; and crucially, that participants, especially religious believers and affiliates, discriminate against hypothetical defendants who take the secular affirmation.”


However, they did state that the “latter effect” is small and does not necessarily imply that taking the affirmation will have a significant impact on all outcomes. However, in heavily contested cases, this ingrained prejudice could be a factor that tips the balance. 

The team then performed a follow-up study of over 1,800 online participants who were asked to watch videos of a mock trial where a man was accused of robbery. One of the videos involved the defendant taking a religious oath before giving evidence, while making an affirmation in the other. The participants were asked to act as pseudo-jurors and were also asked to either swear an oath or affirm that they would try the defendant based on evidence and in good faith. 

Overall, the defendant was not found guiltier when choosing to affirm rather than to swear, and the mock-jurors' belief in God did not seem to affect this. However, those jurors who themselves swore an oath were prejudiced against the affirming defendant. 

These results could have real-world implications for court trials. 


"If taking the oath is seen as a sign of credibility, this could lead to discrimination against defendants who are not willing to swear by God”, Professor Ryan McKay, from the Department of Psychology at Royal Holloway, University of London, said in a statement

"An earlier proposal to abolish the oath in England and Wales was defeated when opponents argued that the oath strengthens the value of witnesses' evidence. This is ironic, as it seems to acknowledge that swearing an oath may give an advantage in court."

Dr. Will Gervais, from Brunel University London, who collaborated on the studies, stated, "The biases we report are subtle, but could potentially tip the balance in cases that could go either way."

The charity Humanists UK issued a statement about the research, calling for changes in the criminal justice system. "Given that prejudice based on religion or belief is still too common in the UK today, it would be best to reform the oath and affirmation system to one that doesn’t reveal this information to jurors," said Richy Thompson, Director of Public Affairs and Policy.


The prejudice against atheists and non-believers is far-reaching, but there is no evidence to show they are any less moral than their religious peers. Interestingly, it seems atheists are more likely to judge to morality based on the consequences of specific actions, while religious people tend to focus on values that support group cohesion. Ultimately, not believing in God has no impact on whether you are a moral or immoral person. 

The study is published in the British Journal of Psychology


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