Personal Agency: The Metaphysics of Mind and Action consists of two parts with five chapters each. Many of the chapters have appeared in print before, but have been revised or rewritten in order to make a single monograph.

The first part of the book is concerned with ways to escape the conclusion of the most popular argument for physicalism: the argument from causal closure. According to this argument, in order to save the causal efficacy of the mental, we have to identify at least some mental events with physical ones because the physical realm is causally closed and physical effects are not systematically causally overdetermined by ontologically distinct causes. According to Lowe, however, there is no version of the principle of causal closure which is not either too weak for the argument to be sound or so strong as to render the argument question begging. Lowe therefore rejects the argument and develops his own account of mental causation according to which mental and physical causation do not contradict but complement each other: Mental causation explains why a certain kind of event, such as raising one's arm, occurs whereas physical causation explains why a particular arm raising occurred. Counterfactually, however, causal priority rests on the side of the mental cause. If the mental cause had not occurred, then neither would there have been a particular arm raising, which is to say that Lowe denies that for any particular physical event P occurring at t there is a sufficient physical cause P* prior to t.

The second part of the book extends the proposed account of mental causation to a libertarian account of free and rational action which avoids the dilemma that a free and rational action is either due to chance, and thus not rational, or else is caused by some reason, and thus is not free after all. Lowe's way to blunt the dilemma consists in combining a theory of free will with elements from theories of both agent causation and volitionism. Against classical accounts of agent causation, however, Lowe argues that it is not the agent simpliciter who in acting freely and rationally initiates new causal chains, but the agent by exercising his power of will. Against classical volitionism he argues that volitions are not causes of free and rational actions, but only causes of action results. Free and rational actions, although they are completely uncaused, are thus not due to chance because they consist in the exercise of the agent's free will to choose to perform an action in the light of the available reasons which, on Lowe's externalist account, are facts and states of affairs in the world. As Lowe says, ‘volitions are causes […] but only insofar as they consist in persons' exercising their power of will and by so doing causing certain events’ (148). Because, as seen above, had certain mental events not occurred, then certain physical effects would not have occurred, Lowe can consistently maintain that without a certain free choice to perform an action, certain physical effects would not have occurred, although there is going to be a physical causal history of the intended effect if the agent successfully performed the action.

A minor problem with Lowe's account of free and rational action consists in the fact that he does not provide an account of how, by exercising one's will, one is able to cause a certain kind of physical event. Instead, he suggests that ‘maybe this is something that is destined forever to remain a mystery to us’ (178). While there surely is a difference between knowing that the will is able to cause physical events and knowing how the will in fact does this, a physicalist is likely to reject Lowe's account for precisely this reason. The physicalist will probably argue that physicalism after all has the resources to account for mental causation on the assumption that at least some mental events are physical events and will take that as an advance over Lowe's account of personal agency.

This aside, I would like to discuss briefly what appears to me to be a bigger problem of the book, namely Lowe's conception of the human person. Lowe's conception of the person suffers unnecessarily from a lack of reflection on the notion of physical and non-physical substances. For a start, according to Lowe, human persons or selves are ontologically distinct, although not separable from human bodies (‘a person and his or her body are […] distinct things, even if they are not separable things’, 102). Because Lowe apparently rejects Cartesian Dualism of immaterial selves and material bodies on the ground that ‘identifying oneself with something non-physical is quite as counterintuitive as identifying oneself with one's physical body or brain’ (21) he calls his theory of the human person Non-Cartesian Substance Dualism. One problem with Lowe's Non-Cartesian Substance Dualism is terminological. If we assume that every substance is either non-physical or else physical, then what Lowe seems to be saying is that the self is a physical substance which is not the human body nor any part of it. Lowe is affirming this when he says that although he ‘very much want[s] to deny that mental states are physical states, […] they are states of something physical – the self’ (22). Taken together with the claim that ‘persons and perhaps some other species of conscious, embodied beings, are the only macroscopic simple substances’ (168), we obtain the conclusion that the self, on Lowe's account, is a macroscopic physical simple substance. This thesis, though, is an ontological substance monism and not a dualism because there is no ontological distinction between the human person and its body at all, only an ontic distinction between different types of physical substances.

A second problem concerns what Lowe then says about the relationship between the physical self and its physical body. According to Lowe, ‘the relationship of embodiment in which a person stands to his or her body [is] sui generis, being neither identity nor constitution and yet implying, as those relations also do, spatial coincidence’ (168). Because the self is a physical substance, the relation between the self and its body entails a rejection of the principle that physical substances are individuated by the space they actually occupy. How, then, can we distinguish between the self and its body, given that both are physical substances? According to Lowe, the self has the power of free will, a power which its body lacks. He could therefore argue that physical substances are individuated by the powers they possess. Since, however, the power of free will is a non-physical power, and since the self spatially coincides with its body, the self would be the only macroscopic simple physical substance which science in principle cannot detect as such. In other words, the self would be empirically invisible, which in effect means that it has the properties we would assume an immaterial self to exemplify. The dilemma is this: if physical substances are individuated by the space they actually occupy, then the self turns out to be identical with its body, and if physical substances are individuated by the powers they possess, then the self turns out to be an immaterial self (or at least turns out to be hardly indistinguishable from what we expect an immaterial self to be). Can Lowe's main argument for Non-Cartesian Substance Dualism clarify the matter? In order to establish that the self is not its body, Lowe argues that no part of his body, nor his body as such could have a property which he himself has: to be the one and only subject of his experiences. The crucial premise in favour of this thesis is that ‘no entity can qualify as the subject of certain mental states if those mental states could exist in the absence of that entity’ (96). Since, according to Lowe, ‘very many and quite possibly all of my own mental states could exist even if my body as a whole were not to exist’ (97) he concludes that the self is not identical with its body or any part of it. To be clear, according to this argument, the self is not its body because it is conceivable that the self exists as the subject of his experiences without its body existing. Now, arguments don't come much more Cartesian than this! Lowe must have recognised this because he qualifies what he means by saying that the self can exist if its body as a whole were not to exist. This only means that ‘even if certain parts that my body actually possesses were not to exist [he could still exist as the subject of his experiences, BPG]’ (97). The latter claim, however, is not a qualification of the former one but a completely different and much weaker statement. The problem is that Lowe yet takes the weaker claim to indicate the stronger conclusion: he takes the weaker claim to ‘indicate[…] that my body as a whole cannot qualify as the subject of all and only my own mental states and so cannot be identified with me’ (97). But this conclusion does not follow, endorsing the downgraded qualification. Deploying the qualification as a premise in the argument it only follows that the self is not identical with certain actual parts of its body. Without the qualification the argument indeed shows that the self cannot be identified with its body as a whole, but only at the price of endorsing something pretty much indistinguishable from Cartesian Dualism, if that means that the self can exist without any of the relevant physical entities existing.

The problem with Lowe's conception of the human self is that Lowe wishes to distinguish between the self and its body without commitment to Cartesian Dualism. However, his actual argument for that very distinction between the self and its body either leads to Cartesian Dualism or does not even get the distinction between the self and its body of the ground.

There might be a very simple solution to Lowe's problem. His resistance to Cartesian Dualism seems to rest on the assumption that any form of Cartesian Dualism is committed to the claim that the self cannot exemplify physical properties. This, however, is not true and the solution might just rest in a proper analysis of physical and non-physical substances. Elsewhere, I argue that a non-physical substance might just be a substance which exists at least in one possible world without exemplifying a physical property in that world, whereas a physical substance exemplifies physical properties in any world in which it exists. On this assumption, Lowe could endorse the sound version of his argument for the ontological distinction between the human person and its body while at the same time he could hold that the self contingently exemplifies physical properties. This, at least it seems to me, would fit well into his overall theory.

Although I see a severe problem with Lowe's theory of the self, Lowe's Personal Agency: The Metaphysics of Mind and Action is an excellent book which could be recommended to anyone interested in the refutation of physicalism, or in the very possibility of rational human agency. Lowe is not only aware of the relevant recent philosophical debates, (which have already profited from his previous publications) but he is also aware of the relevant discussions in the sciences, knowing, and this is rare today, where philosophy starts, and, more importantly, where science ends. I can only agree with him, when he says [that] ‘we should be prepared to acknowledge that a priori metaphysical argumentation might in the end provide the best, or indeed the only, hope for a resolution of the mind-body problem’ (78). After a century reigned by logical positivists, post-modernists and the like, Lowe establishes himself at the forefront of the revival of serious a priori metaphysics. To disagree reasonably with such metaphysics is to engage in it.