1 Introduction

The way people produce arguments is doubly problematic. First, they mostly find arguments for their own side. Second, these arguments tend to be relatively weak. The first trait of argument production—the confirmation bias or myside bias—has been the topic of much attention (see, e.g., Nickerson, 1998). The later has been comparatively neglected, but is well supported by the existing evidence. When asked to justify their points of view, many participants can only generate arguments that make "superficial sense" (Perkins, 1985, p. 568), and they fail to offer genuine evidence (Kuhn, 1991). Similar results have been observed in social psychology (Nisbett & Ross, 1980) and in the study of formal reasoning (Evans, 2002). When people face simple problems ranging from the Wason selection task (Wason, 1966) to the Cognitive Reflection Test (Frederick, 2005), they typically start with a wrong intuition, which the subsequent reasoning fails to correct in most cases. This happens not only because people mostly look for arguments supporting their intuition (see Ball, Lucas, Miles, & Gale, 2003), but also because they are satisfied with the arguments they find—arguments that must be flawed given that they support a logically or mathematically invalid answer. Summarizing the perspective of dual process theories, Kahneman (2011) explains this poor performance of reasoning by the fact that "System 2 is sometimes busy, and often lazy" (p. 81): Reasoners do not make the effort that would be required to produce better arguments (see also, e.g., Evans, 2008).

This laziness, however, does not seem to apply to all arguments. When people evaluate other people's arguments—in particular, if they disagree with their conclusion—they appear to be more careful, and to mostly accept strong arguments. This result has been observed in research on persuasion and attitude change (for a review, see Petty & Wegener, 1998), and in Bayesian studies of argumentation (Hahn & Oaksford, 2007). Sound argument evaluation skills are also indicated by the fact that participants are convinced by arguments supporting the valid answer to reasoning problems such as those mentioned above (for the Wason selection task, see Moshman & Geil, 1998; for the CRT, see Trouche, Sander, & Mercier, 2014; and, more generally, Laughlin, 2011).

When it comes to evaluating others' arguments, the evaluation is most likely to be thorough when participants disagree with the argument's conclusion. When they agree with an argument's conclusion, not only are participants more likely to find the argument valid, but they also discriminate less between valid and invalid arguments, showing a relaxation of their evaluative criteria (Evans, Barston, & Pollard, 1983). Given that when participants produce arguments, they agree with the argument's conclusion, a more general way to frame the asymmetry between argument production and argument evaluation is as follows. When people agree with an argument's conclusion, they tend to evaluate it only superficially—this includes others' arguments whose conclusion one agrees with or arguments one produces. When people disagree with an argument's conclusion, they tend to evaluate it more thoroughly. Reasoning would thus only be selectively lazy.

The asymmetry that has the greatest ecological validity is that between the production of arguments and the evaluation of arguments whose conclusion one disagrees with—this is what happens in a standard exchange of arguments in which two or more people try to convince each other of their respective viewpoints. However, this asymmetry has only been indirectly demonstrated, from comparisons of disparate studies, and it is confounded by the fact that argument quality varies between different contexts and interlocutors. A convincing demonstration of this asymmetry would instead involve participants evaluating their own arguments as if they were someone else's. We would then expect that the participants would reject many of the arguments they deemed good enough to produce, if they thought the arguments came from someone else and they disagreed with their conclusion. Moreover, they should be better at discriminating between their own good and bad arguments when they think they are someone else's and they disagree with their conclusion.

To test this prediction, we relied on the choice blindness paradigm, in which participants are led to believe that they have provided a given answer when in fact they answered something else. For example, in Hall, Johansson, and Strandberg (2012), the participants rated to what extent they agreed with moral issues, such as "If an action might harm the innocent, it is morally reprehensible to perform it." Using a sleight of hand, the participants' answers were at times reversed: If they had indicated that they agreed with the preceding statement, their answer now read that they agreed with an opposite statement (i.e. "… it is morally permissible…"). Participants were then asked to defend their positions, so that they would sometimes be asked to defend a moral position that was the opposite of their originally stated