When solving reasoning tasks such as the Cognitive reflection test (CRT) or the Belief bias syllogisms (BBS), people can do it in four different ways depending on whether they detected the conflict or not and whether they were accurate or not. Specifically, one can detect the conflict and be accurate, detect the conflict but be inaccurate, fail to detect the conflict but still be accurate or fail to detect the conflict and be inaccurate. In this study, we investigated whether the individual differences in intelligence, numerical ability, math knowledge and analytic thinking dispositions underpin these different approaches to solving reasoning tasks. Generally, we found that very accurate conflict non-detectors were the most intelligent, numerate and knowledgable of all the groups. On the contrary, inaccurate conflict non-detectors were the least intelligent, numerate and knowledgable, with the other two groups somewhere in between these two. However, the conclusions depended on what reasoning tasks were used and how the conflict detection was operationalized. We argue that these individual differences indicate that different people solve reasoning tasks in qualitatively different ways and that this calls in question the validity of reasoning tasks. Namely, we hypothesize that reasoning tasks could be measuring different constructs for different people. Specifically, we hypothesize and offer preliminary evidence that the CRT at least somewhat assesses reflection for those lower on cognitive abilities, but not at all for those very intelligent and numerate participants. We discuss how these findings relate to contemporary dual-process theories and validity of reasoning tasks and offer some speculations and suggestions.