The greatest strength of Byrne's (Reference Byrne2005) book is that it explores a particular aspect of a broader question: namely, the extent to which creative forms of cognition spring from the same fundamental processes as “ordinary,” non-creative cognition. The issue is critical because so much of human cognition is creative and yet, historically, comparatively little theoretical and empirical effort has been expended to examine creative functioning (Finke et al. Reference Finke, Ward and Smith1992; Sternberg & Lubart Reference Sternberg and Lubart1996; Reference Sternberg, Lubart and Sternberg1999; Ward et al. Reference Ward, Smith, Finke and Sternberg1999).

Byrne has marshaled considerable evidence for the ideas that human reasoning is rational, that imagination is rational, and, most importantly, that both types of cognitive functioning may be governed by the same small set of principles. In extending the analysis to other aspects of creative functioning, including conceptual expansion (e.g., see Ward Reference Ward1994) and conceptual combination (e.g., see Wisniewski Reference Wisniewski1997), however, some questions arise. More specifically, Byrne speculates that when people must generate new instances of already existing categories (e.g., novel science fiction creatures), they consider true possibilities and few possibilities. That is, their thinking is governed by the same principles that guide logical and counterfactual reasoning in the types of problems considered elsewhere in the book. The principles seem to be proposed as playing a causal role in conceptual expansion just as they do in counterfactual reasoning. To illustrate with one of Byrne's examples, in generating novel birds, people might retrieve sparrows rather than penguins because the former are “true” instances that possess wings and feathers, whereas the latter are not “true” in that they lack those attributes.

It has been shown that the majority of people assigned the task of generating new instances rely on highly representative category exemplars (e.g., hammers as a basis for devising new tools) (Ward et al. Reference Ward, Patterson, Sifonis, Dodds and Saunders2002). To the extent that those more representative exemplars are more “true” (i.e., possess more of the category's characteristic attributes), the data could be interpreted as supportive of the “true possibilities” principle. However, there are two problems with this interpretation. First, sharing more characteristic properties is a very different sense of being a true possibility than, for example, the true states of affairs posed in standard logical and counterfactual problems (i.e., the true states of affairs implied by if–then statements). The danger is that by stretching the meaning of “truth” it becomes a slippery construct that is no longer of tight explanatory value.

The second problem is that, even if shared characteristic attributes can be defended as being the same type of trueness as in logical implication, the connection between it and the use of an exemplar in creative generation may be entirely correlational. The proposed tendency to consider true possibilities may not be what causes people to retrieve and rely on representative exemplars. Rather, the most accessible instances in a category may only coincidentally happen to possess more characteristic attributes, but their accessibility may be determined by any number of factors other than possessing those attributes. To extend this point, once variability due to accessibility is taken into account, typicality (presumably linked to shared attributes) is not positively related to the tendency for people to retrieve and rely on specific category exemplars in creative generation (Ward et al. Reference Ward, Patterson, Sifonis, Dodds and Saunders2002). Hence, there is reason to doubt trueness, in the sense of possessing certain characteristics of the category, as a causal factor in conceptual expansion.

In a related way, Byrne seeks to account for interpretations of conceptual combinations by way of the same types of principles. Consider that a “cactus fish” might be interpreted as a fish with spikes or prickles. According to Byrne's account, this may be due to people only representing the single (presumably true) possibility of a cactus' spines. Again, there is a question of whether “true” possibility in the sense of distinctive properties is really the same as true possibility as considered in most logic problems. And, again there is a question of whether “considering true possibilities” serves as a casual mechanism, or only happens to be correlated with the myriad properties of concepts that affect the interpretation of conceptual combinations (Bock & Clifton Reference Bock and Clifton2000; Estes Reference Estes2003; Gagné Reference Gagné2000; Gagné et al. Reference Gagné, Spalding and Ji2005; Murphy & Wisniewski Reference Murphy and Wisniewski2006; Wilkenfeld & Ward Reference Wilkenfeld and Ward2001; Wisniewski Reference Wisniewski1997; Wisniewski & Love Reference Wisniewski and Love1998). That is, it is the structure of the concepts and the effect of that structure on retrieval and combination that drives interpretation, rather than the principles of representing true and few possibilities.

Explaining the mechanisms that govern conceptual combination is critical to an understanding of creative functioning, because combinations are often mentioned as a source of creative discovery and invention (e.g., see Costello & Keane Reference Costello and Keane2000; Reference Costello and Keane2001; Rothenberg Reference Rothenberg1979; Scott et al. Reference Scott, Lonergan and Mumford2005; Thagard Reference Thagard, Asquith and Kitcher1984). Similarly, a good deal of creative behavior involves conceptual expansion. As a purely descriptive account, it is appropriate to note the types of connections that Byrne has pointed out that may help to characterize these phenomena. However, offering the principles as general explanatory ones for multiple forms of creative cognition is more problematic.

Finally, Byrne is appropriately cautious in distinguishing between counterfactual imagination and more extraordinary forms of imagination and creativity, such as writing novels and creating symphonies. It is essential not to overextend the principles being proposed to domains of creative functioning for which they are plainly not applicable. However, it should also be noted that many extraordinary forms of creativity arise from continued, recursive, extensive application of basic processes. An example described by the noted fantasy author, Stephen Donaldson (Reference Donaldson1991), is that he got the idea for his award-winning novels about Thomas Covenant: The Unbeliever by combining the concepts of unbelief and leprosy. The combination sparked his thinking, but he then spent months on developing characters, scenes, maps, and so on (Ward Reference Ward2001). Presumably, the bulk of that continued creative effort which led to his extraordinary novels was underpinned by ordinary cognitive processes of analogy, mental models, imagery, and so forth. Therefore, although restraint is in order, considering just how far a basic process account can be extended in service of explaining extraordinary creativity is definitely a useful exercise.