The human imagination remains one of the last uncharted terrains of the mind. People often imagine how events might have turned out “if only” something had been different. The “fault lines” of reality, those aspects more readily changed, indicate that counterfactual thoughts are guided by the same principles as rational thoughts. In the past, rationality and imagination have been viewed as opposites. But research has shown that rational thought is more imaginative than cognitive scientists had supposed. In The Rational Imagination, I argue that imaginative thought is more rational than scientists have imagined. People exhibit remarkable similarities in the sorts of things they change in their mental representation of reality when they imagine how the facts could have turned out differently. For example, they tend to imagine alternatives to actions rather than inactions, events within their control rather than those beyond their control, and socially unacceptable events rather than acceptable ones. Their thoughts about how an event might have turned out differently lead them to judge that a strong causal relation exists between an antecedent event and the outcome, and their thoughts about how an event might have turned out the same lead them to judge that a weaker causal relation exists. In a simple temporal sequence, people tend to imagine alternatives to the most recent event. The central claim in the book is that counterfactual thoughts are organised along the same principles as rational thought. The idea that the counterfactual imagination is rational depends on three steps: (1) humans are capable of rational thought; (2) they make inferences by thinking about possibilities; and (3) their counterfactual thoughts rely on thinking about possibilities, just as rational thoughts do. The sorts of possibilities that people envisage explain the mutability of certain aspects of mental representations and the immutability of other aspects.

Byrne's book is intended to explain why people imagine the things they do when they create alternatives to reality. Two fruitful areas of further research are: (1) How can her approach explain dreams and daydreams? (2) What is the developmental time course of the child's understanding of reality and imagination?

If imagination is guided by the same principles as rational thoughts, then we ought not to stop at the way people make inferences to get insights about the workings of imagination; we ought to consider as well the way they make rational choices. This broader approach accounts for the puzzling effect of reasons to act on the mutability of actions.

The notion of mutation is applicable to the generation of novel designs and solutions in engineering and science. This suggests that engineers and scientists have to work against the biases identified in counterfactual thinking. Therefore, imagination appears a lot less rational than claimed in the target article.

Causal and counterfactual thoughts are bound together in Byrne's theory of human imagination. We think there are two issues in her theory that deserve clarification. First, Byrne describes which counterfactual possibilities we think of, but she leaves unexplained the mechanisms by which we generate these possibilities. Second, her exploration of “strong causes” and enablers gives two different predictions of which counterfactuals we think of in causal scenarios. On one account, we think of the counterfactuals which we have control over. On the other, which counterfactuals we think of depends on whether something is a strong cause or an enabler. Although these two accounts sometimes give the same predictions, we present cases in which they differ, and we would like to see Byrne's theory provide a way of reconciling these differences.

Ruth Byrne presents a three-step argument to the conclusion that counterfactual imagining is rational. Insofar as this argument is valid, the conclusion is weaker than it seems. More importantly, it does not represent the central contributions of this book – contributions that, if anything, point instead to what is irrational about counterfactual imagining.

Counterfactual thinking may be described as disciplined, realistic, and rational, but we move a step further to describe a theoretical perspective centering on behavior regulation. According to this perspective, counterfactual thinking primarily centers on coordination of ongoing behavior. In short, most “if only” thoughts in daily life center on the acquisition of goals; hence, counterfactual thinking may be illuminated by considering the large literature on goal cognition.

Byrne's approach to the semifactual conditional captures the reasoning data. However, we argue that it does not account for the processes or principles by which people arrive at representations of even-if conditionals, upon which their reasoning is said to be based. Drawing upon recent work on the suppositional conditional we present such an account.

Why do humans imagine alternatives to reality? The experiments conducted by Byrne explain the mental mechanisms we use when we do just this – that is, imagine one, or more, alternative reality. But why do we do this? The general reason is to give ourselves an explanation of the world, to tell stories; at times to console ourselves, and at times to despair. A good story is not only based on a description of what happened, but also hints at, or explains, what might have happened. Depending on our aim, we construct different kinds of counterfactuals. In all cases, however, we are faced with constraints. These constraints are specific to a given domain of beliefs and use of counterfactuals.

In The Rational Imagination, Byrne proposes a mental models account of why causal and counterfactual thinking often focus on different antecedents. This review critically examines the two central propositions of her account, finding both only weakly defensible. Byrne's account is contrasted with judgment dissociation theory, which offers a functional explanation for differences in the focus of causal and counterfactual thinking.

Byrne (2005) assumes that counterfactual thinking requires a comparison of facts with an imagined alternative. In our view, however, this assumption is unnecessarily restrictive. We argue that individuals do not necessarily engage in counterfactual simulations exclusively to evaluate factual reality. Instead, comparative evaluation is often suspended in favor of experiencing the counterfactual simulation as if it were real.

Byrne's book makes a strong case for the important role of imagination as a creator of possibilities that are used to understand complex relations, while remaining rational. I suggest that imagination also serves a critical developmental role by creating possibilities that are not rational, and that act to modify the nature of the cognitive processes that are used to define rationality.

Byrne implies that working memory development underpins children's ability to represent counterfactuals as possibilities at 3 to 4 years of age. Recent findings suggest that (1) developments in the ability to consider alternatives to reality in children of this age are underpinned by improvements in inhibitory control, not working memory, and (2) children do not develop an understanding of counterfactuals as possibilities until mid-childhood.

Imagination and rational thought may be guided by identical principles, and Byrne's (2005) analysis expertly synthesizes a diverse literature on counterfactual thinking. Further attention should be paid to metacognitive experiences, like ease or difficulty of thought generation, which accompany the imaginative process. Only by considering metacognitive experiences along with the content of what people imagine can we fully understand imagination.

Byrne's criteria for considering imagination rational do not accord with standard notions of rationality. A different criterion – that is, the correspondence between an inference strategy and its domain of application – is offered and illustrated with recent work on possibility judgment. This analysis suggests that, although imagination can be put to rational purposes, imagination itself should not be considered rational.

We critique the distinction Byrne makes between strong causes and enabling conditions, and its implications, on both theoretical and empirical grounds. First, we believe that the difference is psychological, not logical. Second, we disagree that there is a strict “dichotomy between the focus of counterfactual and causal thoughts.” Third, we disagree that it is easier for people to generate causes than counterfactuals.

Byrne has written a terrific book that is, nevertheless, based on a mistaken assumption – that imagination is largely rational. I argue in this commentary that her book follows very well, if one accepts her assumption of rationality, but that the bulk of the evidence available to us contradicts this assumption.

How the rational imagination develops remains an open question. The ability to imagine emerges early in childhood, well before the ability to reason counterfactually, and this suggests that imaginative thought may facilitate later counterfactual ability. In addition, developmental data indicate that inhibitory control may also play a role in the ability to reason counterfactually.

Byrne (2005) demonstrates that reasoning and imagination are logical and governed by the same processing principles. In extending those principles to other forms of imaginative functioning, however, problems arise. The meaning of “true possibility” is stretched, and the causal role of the principles is not well established. Nevertheless, consideration of the extent to which ordinary cognitive processes govern creative functioning is valuable.

When creating alternatives to reality, people often feel emotions in response to these imaginary worlds. I argue that these emotions serve an important purpose. They signal how the world could have been better and prioritize actions to bring this better world about.