If you could meet yourself, would you always agree with yourself?

You might hope so. But according to a new study, many people will reject their own arguments - if they're tricked into thinking that other people proposed them. The paper, published in Cognitive Science, is called The Selective Laziness of Reasoning and it's from cognitive scientists Emmanuel Trouche and colleagues. By "selective laziness", Trouche et al. are referring to our tendency to only bother scrutinizing arguments coming from other people who we already disagree with. To show this, the authors first got MTurk volunteers to solve some logic puzzles (enthymematic syllogisms), and to write down their reasons (arguments) for picking the answer they did. Then, in the second phase of the experiment, the volunteers were shown a series of answers to the same puzzles, along with arguments supporting them. They were told that these were a previous participant's responses, and were asked to decide whether or not the "other volunteer's" arguments were valid. The trick was that one of the displayed answers was in fact one of the participant's own responses that they had written earlier in the study. So the volunteers were led to believe that their own argument was someone else's. It turned out that almost 60% of the time, the volunteers rejected their own argument, and declared that it was wrong. They were especially likely to reject it when they had, in fact, been wrong the first time. Trouche et al. conclude that

Participants proved critical of their own arguments when they thought that they were someone else's, rejecting more than half of the arguments. They also proved discriminating: they were more likely to reject their own arguments for invalid answers than their own arguments for valid answers... These experiments provide a very clear demonstration of the selective laziness of reasoning. When reasoning produces arguments, it mostly produces post-hoc justifications for intuitive answers, and it is not particularly critical of one's arguments for invalid answers. By contrast, when reasoning evaluates the very same arguments as if they were someone else's, it proves both critical and discriminating.

Does this mean that human reasoning is broken? No, the authors say - selective laziness might actually be a good thing, as it helps generate conversations:

Opening a discussion with a relatively weak argument is often sensible: It saves the trouble of computing the best way to convince a specific audience, and if the argument proves unconvincing, its flaws can be addressed in the back and forth of argumentation. Indeed, the interlocutor typically provides counter-arguments that help the speaker refine her arguments in appropriate ways... As a result, the laziness of argument production might not be a flaw but an adaptive feature of reasoning. By contrast, people should properly evaluate other people's arguments, so as not to accept misleading information - hence the selectivity of reasoning's laziness.

There's just one caveat to these results. During a debriefing phase after the test was over, about half of the participants reported that they noticed the "trick" in which their own arguments were passed off as someone else's. The other half of the volunteers did not report suspecting anything, and those "non-detectors" were the ones whose data were included in the final analysis. The people who spotted the trick were excluded; these "detectors" tended to be people who had done well on the logic tests. So a skeptical interpretation of these results is that some of the participants were just not paying much attention, either to the problems or to their own answers.

Trouche E, Johansson P, Hall L, & Mercier H (2015). The Selective Laziness of Reasoning. Cognitive Science PMID: 26452437