BEHAVIORAL AND BRAIN SCIENCES (1999) 22, 809–869 Printed in the United States of America A neuron doctrine in the philosophy of neuroscience Ian Gold Institute of Advanced Studies, Australian National University, Canberra ACT 0200, Australia [email protected] www.coombs.anu.edu.au/Depts/RSSS/People/IanGold.html; Department of Ophthalmology, Royal Victoria Hospital, Room H414, 687 avenue des Pins ouest, Montreal, Quebec, Canada H3A 1A1 [email protected] Daniel Stoljar Department of Philosophy and Institute of Cognitive Science, University of Colorado, Boulder, CO 80309 [email protected]; Institute of Advanced Studies, Australian National University, Canberra ACT 0200, Australia [email protected] www.coombs.anu.edu.au/Depts/RSSS/People/Stoljar.html Abstract: Many neuroscientists and philosophers endorse a view about the explanatory reach of neuroscience (which we will call the neuron doctrine) to the effect that the framework for understanding the mind will be developed by neuroscience; or, as we will put it, that a successful theory of the mind will be solely neuroscientific. It is a consequence of this view that the sciences of the mind that can- not be expressed by means of neuroscientific concepts alone count as indirect sciences that will be discarded as neuroscience matures. This consequence is what makes the doctrine substantive, indeed, radical. We ask, first, what the neuron doctrine means and, second, whether it is true. In answer to the first question, we distinguish two versions of the doctrine. One version, the trivial neuron doctrine, turns out to be uncontroversial but unsubstantive because it fails to have the consequence that the nonneuroscientific sciences of the mind will eventually be discarded. A second version, the radical neuron doctrine, does have this consequence, but, unlike the first doc- trine, is highly controversial. We argue that the neuron doctrine appears to be both substantive and uncontroversial only as a result of a conflation of these two versions. We then consider whether the radical doctrine is true. We present and evaluate three arguments for it, based either on general scientific and philosophical considerations or on the details of neuroscience itself, arguing that all three fail. We conclude that the evidence fails to support the radical neuron doctrine. Keywords: Churchlands; classical conditioning; cognitive neuroscience; Kandel; learning; materialism; mind; naturalism; neurobiology; neuron doctrine; neurophilosophy; philosophy of neuroscience; psychology; reduction; theoretical unification 1. Introduction it will one day explain the mind is obviously one of the more fundamental and ambitious claims that could be made Among those who reflect on the nature of neuroscience, about any science. If, as the neuron doctrine alleges, neu- there is a view about its scope and limits which we will call, roscience will explain the mind, that would make it tremen- with a certain amount of historical license, the neuron doc- dously important to scientists and nonscientists alike. Any trine.1 Roughly, the neuron doctrine is the view that the discussion of the foundations of neuroscience, therefore, framework within which the science of the mind will be de- must involve an assessment of the neuron doctrine. veloped is the framework provided by neuroscience; or, as we put it, that a successful theory of the mind will be a solely ian gold is a fellow in the Vision Research Unit at 2 neuroscientific theory. The idea is not, of course, that neu- McGill University. In January 2000 he takes up a faculty roscience will explain everything about the mind; perhaps position in the Department of Philosophy at Monash there are aspects of the mind we will never explain. The University in Melbourne. idea is rather that, to the extent that we will achieve a sci- daniel stoljar is Assistant Professor of Philosophy at entific understanding of mental or psychological phenom- the University of Colorado, at Boulder, and a Research ena at all, neuroscience will be the science that achieves it. Fellow at the Institute of Advanced Studies, Australian According to the neuron doctrine, in the race to explain the National University, Canberra. He is the author of a mind, smart money is on neuroscience. number of articles in philosophy of mind, metaphysics, There are at least three reasons for thinking that the neu- and meta-ethics. ron doctrine so described is important. First, to claim that © 1999 Cambridge University Press 0140-525X/99 $12.50 809 Gold & Stoljar: A neuron doctrine Second, the neuron doctrine seems to be strongly sup- olutionary consequence of doing so. In section 2, we dis- ported by science and philosophy. This might be brought out tinguish two versions of the doctrine, one trivial and one in the following way.3 Many scientists and philosophers ad- radical, and we argue that these versions have not been here to the methodological view known as naturalism. Ac- clearly distinguished in the literature on neuroscience. We cording to naturalism, to the extent that we will be able to then turn to three arguments for the radical version of the understand the world, it will be empirical science (and not, doctrine, each prompted by scientific claims or views in the for instance, religion or philosophy) that provides that un- philosophy of science. The first argument, which we call derstanding. Similarly, many scientists and philosophers ad- the argument from naturalism and materialism (sect. 3), is here to the metaphysical view sometimes known as materi- based on a small number of highly plausible claims that we alism. Roughly, materialism holds that psychological events, take most neuroscientists and philosophers accept. The sec- states, and processes are nothing more than events, states, ond argument, which we call the argument from unification and processes of the brain.4 Given these two views, and treat- (sect. 4), attempts to defend the neuron doctrine by ap- ing neuroscience by definition as the science of the brain, it pealing to considerations about the development of scien- seems inevitable that the neuron doctrine is true: if the mind tific theories. The final argument, which we call the argu- is the brain, and if neuroscience is the science of the brain, ment from exemplars (sect. 5), looks to neuroscience itself then it is practically5 a fact of logic that neuroscience is the for support of the radical version of the neuron doctrine. To science of the mind, and that it alone will explain what can evaluate this argument, we consider one case of neurosci- be explained about the mind. Indeed, from this point of view, entific theory at some length, namely, the theory of ele- it is difficult to deny the neuron doctrine without sounding mentary learning in the marine snail Aplysia from Eric – as the philosopher Frank Jackson (1982) has put it in a re- Kandel and his colleagues. These arguments do not exhaust lated context – like someone who believes in fairies. all the ones that might be offered in defense of the neuron Finally, proponents of the neuron doctrine often suggest doctrine, but we have chosen to discuss them because they that their view apparently has important, and potentially are all highly plausible, because they appeal to principles devastating, consequences for our current practice of at- respected by neuroscientists and philosophers alike, and tempting to construct a scientific understanding of the because they point up important conceptual features of mind, and perhaps even for intellectual domains further neuroscience and its place among the sciences of the mind. afield, such as the structure of scientific theories, the cor- We conclude, in section 6, with some remarks about the rect approach to the understanding of the social world, and morals one might draw from our argument. the proper conception of morality, art, and the self.6 This is because, on the face of it, neuroscience is not the science of the mind, as the neuron doctrine suggests, for the simple 1.1. Who holds the neuron doctrine? reason that it is not the only science of the mind. On the For the purposes of our discussion, we will take the chief contrary, there are plenty of apparently non-neuroscientific proponents of the neuron doctrine to be the philosopher- disciplines, such as psychology, psychophysics, linguistics, neuroscientists Patricia S. and Paul M. Churchland. There ethology, and the like – sciences we will group together as are two reasons for this. First, as we shall see, the Church- the psychological sciences. If the neuron doctrine is true, lands are particularly clear and knowledgeable advocates of what are we to make of them? For proponents of the neu- the doctrine.7 Second, because neuroscientists themselves ron doctrine, the inevitable result of tracing out its conse- tend to be reticent about expressing metascientific com- quences is that the psychological sciences must be relegated mitments in anything other than popular or quasi-popular to a second-rate, or placeholder, status. Of course, one publications (some of which we canvass below), it has might fail, or simply refuse, to draw this consequence, but, largely been left to the Churchlands to articulate in a tech- from the point of view of the neuron doctrine, this could nical way the status and commitments of neuroscience. In- only constitute a failure of intellectual nerve and, anyway, deed, more than anyone else on the contemporary scene, does nothing to undermine the importance of the doctrine the Churchlands are responsible