Barbey & Sloman (B&S) relegate the logical rule of the excluded middle to a footnote. But this logical rule is necessary for natural sampling. Making the rule explicit in a logical tree can make a problem easier to solve. Examples are given of uses of the rule that are non-constructive and not reducible to a domain-specific module.

The target article makes an impressive case that nested set operations (NS) facilitate probability computations by helping make clear the relevant natural frequency partitions; however, NS can also contribute to common errors. That NS constitute a general reasoning process is supported by their role in deductive, modal, causal, and other reasoning. That NS are solely a rule-based process is problematic.

Evidence favors the nested sets hypothesis, introduced by fuzzy-trace theory (FTT) in the 1990s to explain “class-inclusion” effects and extended to many tasks, including conjunction fallacy, syllogistic reasoning, and base-rate effects (e.g., Brainerd & Reyna 1990; Reyna 1991; 2004; Reyna & Adam 2003; Reyna & Brainerd 1995). Crucial differences in mechanisms distinguish the FTT and Barbey & Sloman (B&S) accounts, but both contrast with frequency predictions (see Reyna & Brainerd, in press).

Though Barbey & Sloman (B&S) distinguish various frequentist hypotheses, they opt rapidly for one specific dual-process model of base-rate facilitation. In this commentary, I maintain that there are many distinct but related versions of the dual-process theory, and suggest that there is currently little reason to favor B&S's formulation over the alternatives.

Barbey & Sloman (B&S) attribute base-rate neglect to associative processes (like retrieval from memory) that fail to adequately represent the set structure of the problem. This commentary notes that associative responses can also lead to base-rate overweighting. We suggest that the difference between the two patterns is related to the distinction between decisions from experience and decisions from description.

We believe that when assessing the likelihood of uncertain events, statistically unsophisticated people utilize a coarse internal scale that only has a limited number of categories. The success of the nested sets hypothesis may lie in its ability to provide an appropriate set structure of the problem by reducing the computational demands.

Subjects in experiments use real-life strategies that differ significantly from those assumed by experimenters. First, true randomness is rare in both natural and constructed environments. Second, communication follows conventions which depend on the game-theoretic aspects of situations. Third, in the common rhetorical stance of storytelling, people do not tell about the representative but about unusual, exceptional, and rare cases.

Barbey & Sloman (B&S) present five models that account for performance in Bayesian inference tasks, and argue that the data disconfirm four of them but support one model. Contrary to B&S, I argue that the cited data fail to provide strong confirmation or disconfirmation for any of the models.

Ego-justifying, group-justifying, and system-justifying motivations contribute to base-rate respect. People tend to neglect (and use) base rates when doing so allows them to draw desired conclusions about matters such as their health, the traits of their in-groups, and the fairness of the social system. Such motivations can moderate whether people rely on the rule-based versus associative strategies identified by Barbey & Sloman (B&S).

While improving the theoretical account of base-rate neglect, Barbey & Sloman's (B&S's) target article suffers from affect neglect by failing to consider the fundamental role of emotional processes in “real world” decisions. We illustrate how affective influences are fundamental to decision making, and discuss how the dual process model can be a useful framework for understanding hot and cold cognition in reasoning.

Homo sapiens have evolved a dual-process cognitive architecture that is adaptive but prone to systematic errors. Fuzzy-trace theory predicts that nested or overlapping class-inclusion relations create processing interference, resulting in denominator neglect: behaving as if one ignores marginal denominators in a 2 × 2 table. Ignoring marginal denominators leads to fallacies in base-rate problems and conjunctive and disjunctive probability estimates.

The commentaries indicate a general agreement that one source of reduction of base-rate neglect involves making structural relations among relevant sets transparent. There is much less agreement, however, that this entails dual systems of reasoning. In this response, we make the case for our perspective on dual systems. We compare and contrast our view to the natural frequency hypothesis as formulated in the commentaries.

In a dynamic world, mechanisms allowing prediction of future situations can provide a selective advantage. We suggest that memory systems differ in the degree of flexibility they offer for anticipatory behavior and put forward a corresponding taxonomy of prospection. The adaptive advantage of any memory system can only lie in what it contributes for future survival. The most flexible is episodic memory, which we suggest is part of a more general faculty of mental time travel that allows us not only to go back in time, but also to foresee, plan, and shape virtually any specific future event. We review comparative studies and find that, in spite of increased research in the area, there is as yet no convincing evidence for mental time travel in nonhuman animals. We submit that mental time travel is not an encapsulated cognitive system, but instead comprises several subsidiary mechanisms. A theater metaphor serves as an analogy for the kind of mechanisms required for effective mental time travel. We propose that future research should consider these mechanisms in addition to direct evidence of future-directed action. We maintain that the emergence of mental time travel in evolution was a crucial step towards our current success.

Foresight requires not only scenarios constructed from memories, but also adequate incentive to let these scenarios compete with current rewards. This incentive probably comes from the efficacy of the scenarios in occasioning present emotions, which depends not on their accuracy per se but on their uniqueness as compared with other possible occasions for emotion.

Acting in the present in anticipation of the future is argued to be a behavioral correlate of mental time travel (MTT). Yet, it is important to consider how other future-directed behaviors – including planning, delay of gratification, and acts of prospective memory – figure into a theory of MTT and future thinking more broadly. Developmental science can help in this formulation.

The claim that nonhuman animals lack foresight is common and intuitive. I propose an alternative whereby foresight is a gradual continuum in that it is present in animals to the extent that it is needed. A second aspect of this commentary points out that the requirements that the memory that mediates foresight be both specific yet flexible seem contradictory.

Mental time travel and theory of mind develop, both phylo- and ontogenetically, at the same stage. We argue that this synchrony is due to the emergence of a shared competence, namely, the ability to become aware of frames of reference.

A species like ours, whose life critically depends on the ability to foresee, plan, and shape future events, is vulnerable to dysfunction if any one facet contributing to what Suddendorf & Corballis (S&C) call “mental time travel” (MTT) is affected by disease. Although the authors mention brain pathology as a potential cause of disturbed MTT, they fail to explore psychopathological syndromes as a source to better understand the significance of MTT for normal functioning and adaptive behaviour.

Suddendorf & Corballis (S&C) propose that the capacity to flexibly forsee the future was a critical step in human evolution and is accomplished by a set of component processes that can be likened to a theater production. Understanding the brain-bases of these functions may help to clarify the hypothesized component processes, inform us of how and when they are used adaptively, and also provide empirical ways of exploring to what degree these abilities exist and are implemented similarly (or differently) across species.

Suddendorf & Corballis (S&C) argue that episodic memory is the most flexible and recently evolved memory system, and point to the reorganization of prefrontal cortex throughout human evolution as the neuroanatomical substrate. Their approach, however, fails to address the unique role that the hippocampus, a primitive brain region, plays in creating and recalling episodic memories, as well as future event construction.