Nicole Vincent’s provocative post challenges our pessimism about the possible use of neuroscientific evidence to prove specific mens rea in criminal cases. In the chapter Vincent discusses, we mention two other possible uses of neuroscience regarding mens rea that we see as more plausible: proving incapacity to form the relevant mental states, and lie-detection evidence to prove either deceptive behavior or prior knowledge (assuming the empirical and conceptual hurdles we identity can be overcome). We also discuss several other examples in the book where neuroscience may potentially inform legal issues. Even on the issues Vincent discusses, we do not think the challenges to generating probative neuroscientific evidence are necessarily insurmountable. Our focus on the conceptual issues was not meant to resolve what is ultimately an empirical issue—whether neuroscientific evidence provides probative evidence regarding the doctrinal mens rea categories. In this response, we focus on five points to illustrate where we agree and disagree with Vincent’s critique.
1. We agree completely with Vincent’s larger point about correlations between brains states and mens rea. As with lie detection, memory, and other issues we discuss in the book, we do not object to the possibility that neurological evidence may be correlated with the behavior and mental states that make up doctrinal legal categories. Whether such correlations exist, and the plausibility of alternative explanations for the evidence, are empirical issues and make this evidence like all other categories of juridical evidence. Vincent notes that such evidence may correlate with “different phenomenology” of intending and this may correlate with different types of mental states. We would go even further and say that even this phenomenological link is not necessary.
2. Vincent worries that our arguments depend on a failure to grasp U.T. Place’s distinction between definitional and compositional identity between mental states and brain states. This distinction, however, does not map onto our analysis; the conceptual points we make in the book are distinct. In the quote Vincent provides, the claim is that mental states are not defined as brain states but nevertheless may be composed of them. By analogy, hats are not defined as bundles of straw tied together even if this hat may be composed of a bundle of straw. According to Place, confusing these types of identity claims leads one to argue, mistakenly, that because you can imagine a hat not composed of a bundle of straw, therefore hats cannot be composed of bundles of straw. The conceptual limitations we discuss do not rely on this mistaken assumption. Rather, the arguments we critique make mistaken assumptions about the relationships between the brain and the criteria for the legal categories, and this leads to the confusion we note. Continuing with the analogy, we are critiquing claims with a structure like the following: “this is a bundle of straw, so it is a hat,” even when the bundle does not look like a hat and cannot plausibly function as such.
Here is a concrete example regarding mens rea. Suppose a crime requires a mens rea of “knowingly” poisoning a victim to death. Assume that the knowledge requirement is defined as whether the defendant was “practically certain” that the poison would kill the victim. (As we caution in the book, “knowledge” for purposes of a legal category, such as mens rea, may deviate from knowledge as commonly understood or as conceptualized by epistemologists.) Now, suppose someone claims that the defendant’s being “practically certain” is identical with an identifiable brain state. The type of contradiction we pointed out would arise if we were also to ascribe the following belief to the defendant during the crime: “the victim will not die from ingesting this substance.” It is absurd to ascribe the inconsistent beliefs that (1) the defendant is practically certain the result will occur and (2) simultaneously believes it will definitely not occur. But, having a particular brain state is not inconsistent with ascribing the second belief to the defendant. Our point here is perfectly consistent with the first belief having a neurological correlate. We do not object to this kind of token-token identity (or even the possibility of type-type identity). We do, however, object to arguments that rely on mistaken criteria for the concepts that comprise the legal categories (these are not brain states, but they may be correlated with brain states).
3. Vincent raises doubts about our assumption that knowledge is an ability rather than information encoded in the brain. In speaking of knowledge as an ability, we were not offering a Theory of Knowledge or the necessary and sufficient conditions for knowing. Rather ,we were simply pointing out that knowledge (both knowing-how and knowing-that) is typically expressed or manifested in various kinds of abilities (including Nicole’s ability to speak and understand Polish) that those who lack the knowledge do not possess: for example, answering questions correctly, offering correct explanations, correcting mistakes, and performing various kinds of successful actions. We acknowledged at several points that this point may be defeasible: one may sometimes possess knowledge without expressing it, and one may sometimes engage in the successful actions without knowledge. As for the point about knowledge not being information encoded in the brain, we were not making a novel claim about knowledge. Rather, we were making use of one of the great insights of modern epistemology: namely, that whether someone has knowledge depends on conditions external to the person (and, a fortiori, the person’s brain). If two people can have the same true beliefs, the same perceptual experiences, access to the same evidence, and similar underlying brain states—yet one person can have knowledge while the other does not—then knowledge is not in the brain. Differences regarding external epistemic justification, Gettier conditions, and so on (see here for an overview), all make knowledge an issue that depends on more than the person (and the brain).
4. Vincent asks about our theory of mind. She asks, if the mind and the various mental attributes (intention, knowledge) are not in the brain, then where are they? We resist this framing of the question. We reject the idea that the mind is a substance that is located somewhere (indeed, anywhere) in the body. As materialists, we accept that the mind and all mental attributes depend on the brain (along with the rest of the nervous system and the body more generally). What we deny is that the mind is a thing in the body, or even the body as a whole. Rather, it is an array of powers, capacities, and abilities. In honor of the upcoming Final Four games this weekend, consider the following analogy. When some player performs a breathtaking slam dunk, we might reflect on all the conditions that had to be necessary or likely in his brain and the rest of his body to perform that complex action (these connections are undeniable and we do not deny them), but it is confusing, we suggest, to ask, what kind of substance is his ability to slam dunk and where is it located?
5. Finally, we are puzzled by Vincent’s claims about feeling intentions. She appears to agree with us that intentions are not feelings, but she also asserts that intending (as opposed to other mental states) has “a distinct feeling.” We are confused by this. Someone may feel and believe a variety of different things while acting, but we doubt there is any distinct feeling of “intending.” When we raise our arms, we feel our arms go up, but we don’t also feel an intent. Nicole, seriously, what does an intent “feel like”?