Broadly speaking, theories in the philosophy of mind are of two sorts: dualist and materialist. Dualist theories, such as the one associated with French philospher René Descartes, claim that there are two fundamentally different kinds of substances in the world: physical substances such as the body and mental substances such as the mind. In contrast, materialist theories claim that there are only physical substances; hence, on a materialist view, mental states are standardly understood to be physical states of the brain.

Patricia Smith Churchland falls squarely in the materialist camp, believing that the mind should be identified with the brain. In fact, she approaches her study in terms of neither the “mind” nor the “brain” but rather in terms of the “mind-brain.” As its subtitle suggests, Neurophilosophy lays the groundwork for a theory of the mind-brain and, according to Churchland, this theory must be informed not only by philosophical work but also by neuroscientific research. Toward this end, Churchland’s primary aim in the book is to bridge the gap between neuroscience and philosophy, acquainting researchers in these fields with one another.

In this way, Churchland assigns to philosophers an important role in the development of a theory of the mind-brain, but it is important to note that she does not think that the needed philosophical work can be done from the armchair, so to speak. Churchland argues persuasively that an adequate theory of the mind must be informed by empirical research. She thus calls for the rejection of what is usually referred to as “folk psychology,” our commonsense understanding of mental states and processes.

Folk psychology consists of a vast network of rough generalizations, usually invoking propositional attitudes such as beliefs and desires, that explain behavior. For example, two such generalizations are as follows: (1) When a person desires to bring about some state of affairs S and believes that her doing action A is the best way to bring about S, then (other things being equal) she will do A; (2) When a person desires to prevent some state of affairs S and believes that S will result from her doing action A, then (other things being equal) she will refrain from doing A. Philosophers of mind have generally assumed that any adequate theory of the mind must, to at least a significant extent, respect the generalizations of folk psychology and account for the propositional attitudes it posits. Churchland thinks that this assumption is deeply mistaken. Advances in physics came only when physicists were willing to reject many of the commonsense presuppositions of folk physics, and advances in medical science came only at the expense of many of the commonsense presuppositions of folk medicine. Likewise, Churchland argues that we must be willing to reject common sense when it comes to psychology, the science of the mind.

This negative assessment of folk psychology is often referred to as “eliminative materialism.” It was first put forward by Paul Feyerabend in the early 1960’s, but its leading proponents throughout the 1980’s and the 1990’s were Churchland and her husband, Paul. Throughout the second part of Neurophilosophy, Patricia Churchland calls upon much of her husband’s published work on eliminative materialism in an attempt to make her case against folk psychology.

First, Churchland claims that folk psychology should be viewed as a theory. She believes that it then becomes apparent how unsatisfactory it is. Advancing considerations from both neuroscience and philosophy, she argues that the inadequacies of folk psychology require that it must eventually be significantly revised or simply replaced with an alternative theory. The replacement theory she envisions, and for which she attempts to lay the groundwork throughout Neurophilosophy, should ultimately come from a matured neuroscience.

Along these lines, she argues that neuroscience and psychology need to develop in conjunction with each other and, moreover, that they must rely on some philosophical theory to guide this development. Philosophy offers folk psychology as a start, but as the sciences continue their joint endeavor, a new philosophical theory needs to emerge to replace the outmoded folk theory. Painting an apt picture of the codevelopment she envisions, she likens the two sciences to two rock climbers ascending a wide chimney by bracing their feet to the walls and their backs to one another.

Having surveyed the neuroscientific and the philosophic terrain in parts 1 and 2, respectively, in the final part of Neurophilosophy Churchland attempts to survey the theoretical terrain. As she notes, though neuroscientists know a significant amount about the structure of nervous systems, they lack a theoretical framework in which to make sense of their experimental results. Against the claims of many neuroscientific researchers that it is still too early for theorizing, or that theorizing is too abstract, Churchland argues that the organizational and motivational value of theories should not be underestimated. Though much of her book seems to be directed toward philosophers, attempting to convince them of the importance of neuroscience, the opening section of part 3 seems clearly aimed at neuroscientists, attempting to convince them of the importance of philosophy.

According to Churchland, the search for a theory should be guided by the following question: What sort of organization in neuronlike structures could produce the output in question (motor control, visual perception, memory, and so on), given the specified input? An ideal theory, or proto-theory, will have what she calls a “Galilean combination” of simplification, unification, and mathematization. Churchland does not herself offer such a theory, but rather, in the remainder of the book, surveys three theoretical ventures in an attempt to show what shape a unified theory of the mind-brain might take.

The tensor network theory, the first theory that Churchland presents and the one to which she devotes the most attention, targets the problem of sensorimotor control by providing a general framework for understanding the computational architecture of nervous systems. In an attempt to make this very complicated theory accessible, Churchland relies on a cartoon story whose main character is the crablike critter Roger. When Roger spots an object, its position is represented in terms of his visual space. However, to reach the object, he has to represent it in terms of his motor space. The tensor network theory aims to explain how visual space representations can be converted into motor space representations. One important contribution of the theory is its postulation of a nonsentential model of representations, thereby counting directly against the folk psychological presumption in favor of sentencelike symbols in the head. Insofar as philosophers and other cognitive scientists who are proponents of a sentential theory of representation argue that their theory is the only game in town, the tensor network theory shows them wrong and offers what Churchland thinks is a promising alternative.

The second theory that Churchland discusses, stemming primarily from the work of Geoffrey Hinton and Terrence Sejnowski, is a connectionist one. This is the theory she later explores in considerable depth in collaboration with Sejnowski in The Computational Brain (1992). Her brief discussion of this theory aims to show that neuroscientific research counts against a sequential model of cognition; the connectionists offer an alternative model according to which cognition proceeds by parallel processing. Finally, the third theory presented, owing to the work of Francis Crick, addresses the neurobiological mechanisms that underlie visual attention. One reason Churchland highlights this theory in particular is that it serves as an example of the coevolution of neurobiology and psychology.

In the end, however, the details of each of these theories are less important than the picture they present of what a neuroscientific theory could look like, that is, how it would be possible to explain the emergence of macro-level phenomena such as visual attention, learning, and movement from the micro (neuronal) level. Churchland thus concludes on a note of optimism: The end of the twentieth century, in her opinion, is a “monumentally exciting” time. As she notes, “we appear to have embarked on a period when an encompassing scientific understanding of the mind-brain will, in some nontrivial measure, be ours.” The arguments that such a scientific understanding must come from both neuroscience and philosophy are her unique contributions to the endeavor.

The highly technical nature of published neuroscientific research once presented philosophers with an excuse for ignorance. One of the important contributions of Neurophilosophy was to deprive philosophers of this excuse, presenting a sketch of neuroscience that started from scratch but did much more than merely scratch the surface. In a similar vein, the book has served to remind philosophers of the vast wealth of empirical data with which their theories of the mind must be consistent. Part of the impact of Neurophilosophy has been to ease the philosopher out of the armchair and into the empirical world.