In many intellective tasks groups consistently outperform individuals. One factor is that the individual(s) with the best answer is able to convince the other group members using sound argumentation. Another factor is that the most confident group member imposes her answer whether it is right or wrong. In Experiments 1 and 2, individual participants were given arguments against their answer in intellective tasks. Demonstrating sound argumentative competence, many participants changed their minds to adopt the correct answer, even though the arguments had no confidence markers, and barely any participants changed their minds to adopt an incorrect answer. Confidence could not explain who changed their mind, as the least confident participants were as likely to change their minds as the most confident. In Experiments 3 (adults) and 4 (10-year-olds), participants solved intellective tasks individually and then in groups, before solving transfer problems individually. Demonstrating again sound argumentative competence, participants adopted the correct answer when it was present in the group, and many succeeded in transferring this understanding to novel problems. Moreover, the group member with the right answer nearly always managed to convince the group even when she was not the most confident. These results show that argument quality can overcome confidence among the factors influencing the discussion of intellective tasks. Explanations for apparent exceptions are discussed.

Research in cultural evolution has focused on the spread of intuitive or minimally counterintuitive beliefs. However, some very counterintuitive beliefs can also spread successfully, at least in some communities-scientific theories being the most prominent example. We suggest that argumentation could be an important factor in the spread of some very counterintuitive beliefs. A first experiment demonstrates that argumentation enables the spread of the counterintuitive answer to a reasoning problem in large discussion groups, whereas this spread is limited or absent when participants can show their answers to each other but cannot discuss. A series of experiments using the technique of repeated transmission show that, in the case of the counterintuitive belief studied: (a) arguments can help spread this belief without loss; (b) conformist bias does not help spread this belief; and (c) authority or prestige bias play a minimal role in helping spread this belief. Thus, argumentation seems to be necessary and sufficient for the spread of some counterintuitive beliefs. (PsycINFO Database Record

Reasoning research suggests that people use more stringent criteria when they evaluate others' arguments than when they produce arguments themselves. To demonstrate this "selective laziness," we used a choice blindness manipulation. In two experiments, participants had to produce a series of arguments in response to reasoning problems, and they were then asked to evaluate other people's arguments about the same problems. Unknown to the participants, in one of the trials, they were presented with their own argument as if it was someone else's. Among those participants who accepted the manipulation and thus thought they were evaluating someone else's argument, more than half (56% and 58%) rejected the arguments that were in fact their own. Moreover, participants were more likely to reject their own arguments for invalid than for valid answers. This demonstrates that people are more critical of other people's arguments than of their own, without being overly critical: They are better able to tell valid from invalid arguments when the arguments are someone else's rather than their own.

In the absence of other information, people put more weight on their own opinion than on the opinion of others: they are conservative. Several proximal mechanisms have been suggested to account for this finding. One of these mechanisms is that people cannot access reasons for other people’s opinions, but they can access the reasons for their own opinions—whether they are the actual reasons that led them to hold the opinions (rational access to reasons), or post-hoc constructions (biased access to reasons). In four experiments, participants were asked to provide an opinion, and then faced with another participant’s opinion and asked if they wanted to revise their initial opinion. Some questions were manipulated so that the advice participants were receiving was in fact their own opinion, while what they thought was their own opinion was in fact not. In all experiments, the participants were consistently biased towards what they thought was their own opinion, showing that conservativeness cannot be explained by rational access to reasons, which should have favored the advice. One experiment revealed that conservativeness was not decreased under time pressure, suggesting that biased access to reasons is an unlikely explanation for conservativeness. The experiments also suggest that repetition plays a role in advice taking, with repeated opinions being granted more weight than non-fluent opinions. Our results are not consistent with any of the established proximal explanations for conservatism. Instead, we suggest an ultimate explanation—vigilant conservatism—that sees conservatism as adaptive since receivers should be wary of senders’ interests, as they rarely perfectly converge with theirs.

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