Suppose two people tell you the same false story.
The first person knows it is untrue and is deliberately trying to deceive you. The second has no idea whether it is true and has made no effort to check.
Whom would you trust more?
Most people would be highly suspicious of the known liar. They might be less concerned about the careless speaker, reasoning that the claim could still be correct.
New research suggests that this difference matters more than we might expect. Statements made without concern for facts may sometimes influence our beliefs more strongly than deliberate lies — especially when we hear them repeatedly.
Psychologists call this kind of communication "truth-indifferent." The speaker may want to sound informed, fill an awkward silence or offer an opinion despite knowing very little. The statement might be true or false. The defining feature is that accuracy does not matter to the person saying it.
Researchers explored this behavior through three experiments involving more than 800 university students.
In the first experiment, participants rated a series of factual and false statements. They were told that the statements came from an average person, a known liar or someone who did not care whether the information was accurate.
The statements were identical in every group. Only the description of the speaker changed.
Participants trusted the average person most. More surprisingly, they rated claims from the careless speaker as more believable than exactly the same claims from the liar.
The next experiments examined what happened when false statements were repeated.
Repetition creates what psychologists call the "illusory truth effect." When we encounter the same claim several times, it becomes easier for the brain to process. That feeling of familiarity can be mistaken for evidence that the claim is true.
Some participants received a warning before seeing the statements. Others learned only afterward that the source had either lied or spoken without concern for accuracy.
An early warning worked well. When people knew from the beginning that the information might be unreliable, repetition had much less influence.
A late warning was less effective.
Once participants learned that a speaker had lied, they lowered their ratings of the repeated false claims. But when they learned that the speaker had simply ignored the truth, the claims continued to feel surprisingly believable.
A known lie is easy to place in a mental box marked "false." A careless claim is harder to dismiss because it remains uncertain. It might be wrong — but it might also be right. That uncertainty leaves room for familiarity to do its work.
The findings do not mean that careless talk is always more harmful than lying. The experiments used neutral fact-based statements and described sources with simple labels. Real conversations are more complicated, and future research will need to test how people respond to actual behavior.
Still, the study offers a useful lesson. When evaluating information, we should not ask only, "Is this person trying to deceive me?"
We should also ask, "Does this person actually know — or care — whether the claim is true?"
A confident voice can make an uncertain idea sound convincing. Repetition can make it feel familiar. But neither confidence nor familiarity is evidence.