There was a time, more recent than one might imagine, when psychological predicates had a far broader range of application than received philosophical wisdom would allow. As late as the turn of the century, one could find respected publications in which spiders attended, ants grew excited, and microbes made choices. “Psychological phenomena,” it was claimed, could be found “from the simplest cellule to the most complicated organism” (Alfred Binet, The Psychic Life of Micro-Organisms: A Study in Experimental Psychology [Chicago: Open Court, 1889], iii). The practice would decline with the rise of operationalism, but psychological predicates never fully went away. In recent years, they have even seen a resurgence. Spiders are once again attending; single-celled creatures are back making decisions.

For those unfamiliar with the trend, the practice may seem fanciful, even nonsensical. How could a cell even begin to make decisions? If the main argument of Carrie Figdor’s Pieces of Mind is correct, however, it is a very real possibility. Over the course of 10 chapters, she lays out an interpretation of the scientific practice that she terms Literalism. Roughly, the Literalist takes the psychological terms at face value: when publications state that neurons “prefer” they mean that neurons prefer. The terms need not have all connotations they carry when applied to humans—plants and single neurons need not be conscious, for instance—but they will invoke the same basic concepts. Claiming that spiders attend is no different from claiming they walk, and just as it would be anthropocentric to take human gait as definitive, it is anthropocentric to restrict notions like preference to beings like ourselves a priori.

While it might seem counterintuitive, Figdor argues, Literalism has many advantages. For one, it avoids any need to massively revise or reinterpret the science. We need not think that the entomologists are taking poetic license or that decades of neuroscientific advances have been peppered with nonsense (as M. R. Bennett and P. M. S. Hacker, Philosophical Foundations of Neuroscience [Malden, MA: Blackwell, 2003] suggest; more below). It also accords with a picture of conceptual evolution that has emerged in recent philosophical work. Historically, concepts often transition from intuitive notions defined with reference to human capacities to more general, abstract notions (see, e.g., Hasok Chang, Inventing Temperature: Measurement and Scientific Progress [Oxford: Oxford University Press, 2004]). Yet, the better part of the text is concerned not with the positive case for Literalism but with the negative case against its competitors. Treating these uses of psychological predicates as literal may feel odd for contemporary philosophers, but it is the best available option.

Figdor considers three alternatives to Literalism, ordered from most to least revisionary. The first, instantiated by Bennett and Hacker’s discussion of neuroscience, is the Nonsense view. On this account, the use of psychological vocabulary is inherently misapplied when used for trees, cells, or other things that cannot behave like humans. Next is the Metaphor view, which—fittingly enough—maintains that such usages accord with nonliteral cases of metaphorical extension (nonliteral to exclude commonplace scientific analogies like the “orbit” of an electron in Bohr’s model of the atom, which can be intended literally). Finally, there is the Technical view, which maintains that scientific applications of psychological predicates are straightforward assertions but that their reference differs from the folk notions to which they are related. Speaking of a neuron’s preferences, in this case, may be likened to speaking of a quark’s color: there are analogies, but the domains are quite different.

In each case, Figdor argues, there emerge interpretive problems. The disputed attributions simply do not behave the way any of the three alternatives would predict. Nonsense statements are characteristically difficult to imagine or interpret. Chomsky’s colorless green ideas, for instance, may feature in a syntactically well-formed sentence but are semantically anomalous. Asked to explain what such a sentence says about the world, one is at a loss. The experimental implications of claims in the best established scientific literature, by contrast, seem relatively straightforward. At the very least, their implications are clear enough to construct research programs and well-confirmed formal models around. Nonliteral metaphor, meanwhile, is generally identified by features like authorial intent and a widely recognized sense of incongruity between target and description. The phrase “Juliet is the sun,” for instance, is readily recognizable as a literally incongruous flourish. Neither feature seems to attend the (frequently dry) assertions made in a standard research article, though. Pragmatically, they also tend to be less stable in their usage. Employed consistently and specifically enough, a metaphor risks becoming literal—indeed, the term “metaphor” itself derives from the Greek term for relocating or carrying something over. When it comes to attributing, say, preferences to neurons, however, the conventions are as established as anything in the literature. Finally, turning to the Technical view, one finds that the sharp boundaries required by the view are often absent. As Figdor notes, technical and nontechnical usage generally do not mix, and a clear sense of punning emerges when one does combine them. “John and his Driver’s license expired last Thursday” is clearly a joke (131). The same is not true of the claim that humans and spiders both attend to movement or that neurons and human subjects habituate, at least not obviously. A phrase like “neural and behavioral responses habituated” may sound stilted, but it is not terribly jocular.

Overall, Figdor makes a strong case. The problems raised for the alternatives are defeasible, but until such time as their advocates have addressed them, the literal reading would seem to have an edge. Granting this, however, one soon notices that the claim is more moderate than it first seems. To start with, the alternatives developed in the text involve some rather strong claims. At base, each maintains “either that the [broadly attributed psychological] terms do not refer or that their reference differs between human and non-human uses” (62). The idea is not simply that the terms’ nonhuman applications tend not to be literal but that the two categories are practically disjoint (79; although, Bennett and Hacker do allow exceptions when nonhuman animals like bonobos behave in human-like ways, see Maxwell Bennett, Daniel Dennett, Peter Hacker, and John Searle, Neuroscience and Philosophy: Brain, Mind, and Language [New York: Columbia University Press, 2007], 20). Assuming a level playing field, such a sweeping denial would seem to demand more than the view that some nonhumans are metaphysically capable of instantiating some psychological properties. What is more, Figdor is careful throughout the text to bracket the actual truth or falsity of individual property ascriptions (e.g., of preferences to neurons; 71). While committed to a face reading of these claims, the Literalist could theoretically take a wide range of positions regarding their accuracy. To say Binet could be right is not to say that he is. One might be optimistic and believe that most are true or pessimistic in thinking most false. Although it would undermine some of the benefits of the Literalist position, one might even be an error theorist, believing that the scientists are systematically making false factual claims rather than true technical or metaphorical assertions.

The main challenge going forward, I suspect, will be in adjudicating between the optimists and pessimists. Judging from remarks early in the text, Figdor leans optimistic (62). Although it is not her primary focus, she also provides some heuristics for assessing a claim’s overall standing. She observes in the third chapter, for instance, that the existence of domain-spanning formal models offers evidence that a property extends beyond its familiar bounds, citing cases like the Lotka-Volterra model of predator-prey relations, which has expanded from tracking foxes and rabbits to plants and even capitalist economic relations. The suggestion is intriguing, but even if we follow her in raising formal models over qualitative analogy—a substantive philosophical position in itself—additional conditions will almost certainly be needed. The fact that many systems can be modeled with, say, logistic functions need not imply that they share more substantial connections, and even sympathetic readers may doubt the strength of the Lotka-Volterra model as an indicator of literal predator-prey relations given its application to chemical oscillations (Alfred J. Lotka, “Analytical Note on Certain Rhythmic Relations in Organic Systems,” Proceedings of the National Academy of Sciences of the USA 6 [1920]: 410–15). At present, it is unclear what the extra ingredients should be. One might look to how many points of analogy there are (i.e., whether the formal specifications are many or few), whether the analogies are distinctive, or whether models capturing different aspects of the domains in question also generalize. Perhaps what is needed is something else entirely. The absence of a clear answer is less a criticism than an invitation for future work, however, and to the extent that such issues are pursued in coming years, it will be in a space cleared by Figdor’s work. Ultimately, Pieces of Mind is a tightly argued book that makes valuable contributions to philosophy of mind, philosophy of science, and the critical integration of the two.