Extremist views on normative rationality fail to address differences in responding owing to intellectual ability or epistemic self-regulation. Individual difference research thus raises serious questions concerning the scientific utility of universal rationality and universal irrationality theories. However, recent data indicate that computational capacity theories do not account adequately for within-subject variability in normative responding, memory-reasoning independence, and instances of ability-normative reasoning independence.

Regardless of the clarity of the patterns they produce, individual differences in reasoning cannot validate norms of rationality. With improved reliability, these correlations will simply reveal which sorts of biases go together and which predict the intelligence of the decision maker. It seems necessary, therefore, to continue efforts to define rational thought independently of intelligence.

In their use of correlations as a means to distinguish between different views on the normative/descriptive gap, Stanovich & West discuss the competence component but neglect the activation-utilization component of performance. Different degrees of motivation may introduce systematic variation that is confounded with the variation explained by cognitive capacity.

Stanovich & West's assumption of discrete System 1 and System 2 mechanisms is questionable. System 2 can be understood as emerging from individuals who score high on several normally distributed cognitive mechanisms supporting System 1. Cognitions ascribed to System 1 and System 2 appear to be directed toward the same evolutionary significant goals, and thus are likely to have emerged from the same selection pressures.

The rationality debate centers on the meaning of deviations of decision makers' responses from the predictions/prescriptions of normative models. But for the debate to have significance, the meaning and functions of normative analysis must be clear. Presently, they are not, and the debate's persistence owes much to conceptual blur. An attempt is made here to clarify the concept of normative analysis.

This commentary focuses on the implications of practical reasoning research for the view of rationality in Stanovich & West's target article. Practical reasoning does not correlate with intelligence or other reasoning tasks. Explanation in decision making terms raises the issue of dilemmas, making it hard to specify the correct norm, when an action can satisfy or conflict with two equally justifiable goals.

While concurring that the evidence from individual differences supports a Meliorist view in the rationality debate, this commentary suggests that (1) the evidence does not clearly support a two-systems interpretation against an interpretation in terms of idiosyncratic differences in mental models, and that (2), especially where interactional processing is concerned, evidence from experimental game theory should also be considered.

Tasks in the adult reasoning literature are designed so that heuristic processing leads one astray and adequate rule-based processing requires explicit knowledge about applicable logical and quasi-logical norms. Other research, however, indicates that appropriate rule-based inferences can be automatic. Individual differences in rationality are largely due to differences in developmental progress toward metacognitive understanding of both heuristic and rule-based inferences.

Stanovich & West's claim that there are two coherent and conceptually distinct types of thinking, System 1 and System 2, is questioned. Some authors equate System 2 with intelligence whereas other do not; and some authors regard the two types of system as distinct while others regard them as lying on a continuum.

Paradoxical individual differences, where a dysfunctional trait correlates positively with some preconceived notion of the normatively correct answer, provide compelling evidence that the wrong norm has been adopted. We have found that logical performance on conditional inference is positively correlated with schizotypy. Following Stanovich & West's reasoning, we conclude that logic is not normative in conditional inference, the prototypically logical task.

The hypothesis of two separate reasoning systems, one subserving individual goals and the other our genes, is theoretically implausible and not supported by the data. As an alternative, I propose a single system for analytical reasoning backed up by simple mechanisms for the selection of relevant information. This system can generate normative behavior as well as systematic deviations from it.

Stanovich & West (S&W) are wrong to think that all “reject-the-norm” theorists simply wish to reduce the normative/descriptive gap. They have misunderstood Issac Levi's reasons for rejecting Tversky and Kahneman's normative assumptions in the “base-rate” experiments. In their discussion of the taxicab experiment, (S&W) erroneously claim that subjects' responses indicate whether they have reasoned in accordance with Bayesian principles or not.

Stanovich & West (S&W) distinguish between evolutionary rationality and normative rationality, and System 1 and System 2 mental processes. They hold that the main function of System 2 has to do with normative and not evolutionary rationality. We ask how System 2 could then be an adaptation, especially given S&W's own work on individual differences.

Although Stanovich & West (S&W) are likely to be criticized for not proposing a process model, results of such a model (fuzzy-trace theory) support many of their conclusions. However, arguments concerning evolution and Gricean intelligence are weak. Finally, developmental data are relevant to rationality, but contradictory results suggest a dual-processes approach that differs from S&W's based on fuzzy-trace theory.

Although a focus on individual differences can help resolve issues concerning performance errors and computational complexity, the understanding/acceptance axiom is inadequate for establishing which decision norms are most appropriate. The contribution of experience to automatic and controlled processes suggests difficulties in attributing interactional intelligence to goals of evolutionary rationality and analytic intelligence to goals of instrumental rationality.

Subjects exhibiting logical competence choices, for example, in Wason's selection task, are exhibiting an important skill. We take issue with the idea that this skill is individualistic and must be selected for at some different level than System 1 skills. Our case redraws System 1/2 boundaries, and reconsiders the relationship of competence model to skill.

Subjects have a rich history of decision making which would be expected to affect reasoning in new tasks. For example, averaging, a strategy that is effectively used in many decisions, may help explain the conjunction fallacy. Before resorting to accounts based on phylogeny, more parsimonious accounts in terms of ontogeny should be explored.

Stanovich & West rely for many of their conclusions on correlations of reasoning tasks with SAT scores. The conclusions they draw are suspect because the SAT is not a particularly good measure of so-called g; g is not necessarily causal, SAT scores are no arbiter of what is true, and in any case it is not suprising that reasoning tests correlate with reasoning tests.

The distinction between abstract (rule-based) and contextual (intuitive) thinking is illustrated by studies of numeric versus linguistic expressions of probability. Verbal probabilities are believed to reflect intuitions that can be adaptive and occasionally normative (e.g., counteracting conjunction errors). Stanovich & West's interpretation of analytic thinking in terms of ability suggests a complementary ability perspective on intuitive thinking.

Violations and biases relative to normative principles of rationality tend to occur when the structure of task environments is novel or the decision goals are in conflict. The two blades of bounded rationality, the structure of task environments and the computational capacities of the actor, can sharpen the conceptual distinctions between the sources of the normative and descriptive gap.