Selves is a wonderfully engaging and provocative book. True, it is long, often complex, and sometimes dense and difficult, with many by-ways and detours en route to its astonishing conclusion – but it is also bold, brilliantly written, and packed full with insights, arguments and speculations. That said, the verdict Strawson reaches with regard to the self is radical, and not easy to accept. He finds that selves do indeed exist, but only in the form of transient episodes of experiencing that are short-lived, probably lasting less than a second. Those of us who find Strawson's initial assumptions plausible, but are reluctant to accept his perturbing conclusion, must decide where best to part company with him; but since the case he makes on behalf of his transient selves is a surprisingly persuasive one, this task is by no means easy or straightforward.

Strawson advocates an experiential approach to the self: he thinks that conscious experience will be right at the heart of any remotely satisfactory account of the self's nature. So far, so traditional – Descartes, Locke, Hegel and Husserl would no doubt have agreed – but Strawson also wants his account of the self to be compatible with a modern, scientifically informed, materialism. Since he rejects reductionism about the experiential, he thinks we should accept that experiences themselves are material in nature. Much of the first half of the book is concerned with isolating the core, essential features of selves, as we conceive them (or as we find them in our experience). After a lengthy sequence of arguments incorporating both a ‘whittling’ phase and a ‘building’ phase, Strawson concludes that these core attributes are small in number: selves are subjects of experience, single, mental, and thing-like – hence his label SESMET (or ‘subject-of-experience-as-single-mental-thing). Features such as personality, persistence and agency are all non-essential. The next question to be addressed is whether anything in reality has what it takes to be a SESMET. After a further complex sequence of investigations and arguments Strawson arrives at his conclusion. Of all the available candidates, it turns out that one fits the bill better than all the others: the strongly unified, short-lived bursts (or phases) of experiencing that Strawson calls thin subjects.

This finding can initially seem strange, to put it mildly. It is commonly assumed that experiences are items that selves (or subjects) possess; if experiences are had by selves, how can experiences be selves? Strawson's response to such concerns is multi-faceted. Selves may just be experiences, but this does not mean they are in any way ontologically suspect or insubstantial. Nothing is more real than experience, he argues, and since experiences are themselves material in nature, they are as real and concrete as any other part or aspect of physical reality – human thin subjects are identical with transient synergetic neural processes. As for whether thin subjects can plausibly be regarded as thing-like, for Strawson the answer is a resounding ‘yes’. The experiential states that constitute thin subjects possess a deep degree of unity, a unity that is ‘unsurpassed’, and this legitimates our taking them to be single things. By way of further support for this claim, Strawson mounts a vigorous case against the traditional duality of substances and attributes: a more adequate metaphysics requires new and different ways of thinking, and these new ways of thinking will not be hostile to viewing experiences as (in effect) substantial. There is a further problem: since they are identical with experiences, thin subjects are not the sorts of things which can persist through periods of unconsciousness. For Strawson this matters little. He argues that there is an appealing conception of ‘subject’ which doesn't require (and indeed rules out) this sort of persistence, a subject which is ‘alive’ in occurrent experiential states, and to be found there and nowhere else.

So selves do exist, albeit in the surprising and unfamiliar form of thin subjects. Since we reach this metaphysically-speaking rock-solid conception of the self via a long detour through phenomenology, Strawson thinks he can say that Kant was at least partly wrong when, in the Paralogisms, he argued that it was impossible to arrive at any metaphysical truths about the real nature of the self by reflecting on the character of our experience.

Perhaps so, but Strawson's selves are strange and unfamiliar beasts, not least because of their brevity. The apparent (or subjective) temporal extension of a thin subject is that of a single specious present, that brief temporal window that enables us, seemingly, to directly apprehend change – Strawson holds that the experiential unity which is essential to selfhood does not extend beyond individual specious presents. Measuring the extension of the specious present is notoriously difficult – linking it to ordinary clock time is but one of the problems – but Strawson tentatively estimates it as around 1/3 of a second's worth of apparent change. However, he suggests that the real objective duration of the episodes of experiencing are briefer by far: perhaps 1/40^th of a second, perhaps a microsecond, perhaps as little as the Planck time of 10⁻⁴⁴ seconds. This tiny interval–whose precise extent, Strawson suggests, only advances in future neuroscience will reveal – is all by way of lifespan a self has to enjoy.

So it is not for nothing that Selves is subtitled ‘An Essay in Revisionary Metaphysics’. Those reluctant to follow Strawson all the way have several alternatives to ponder. Some may be inclined to see Strawsonian selves as a reductio of his assumption that we must take experience as our primary guide to the sort of thing we are. If we take ourselves to be essentially human organisms, for instance, we can be assured of an enduring solid substantiality, even if our consciousness is as disjointed as Strawson suggests. But while there are those who are happy to take this path, it is not for everyone. The idea that consciousness and the self are intimately related – far more so than biological approaches can legitimize – is a powerfully appealing one: it is not for nothing that the notion that selves are essentially subjects of experience has such a long and distinguished philosophical pedigree. If selves are essentially subjects of experience, how do we avoid Strawson's conclusion?

We can start with perhaps the most obvious vulnerability. Strawson's account is supposedly rooted in phenomenology, yet his claim that selves are extremely short-lived comes as a surprise to most of us. But doesn't the fact that it does come as a surprise suggest that something must have gone awry in Strawson's phenomenological investigations? His conclusion that selves typically last less than a second is rooted in a claim about our consciousness: that it takes the form of discrete bursts, whose objective duration is extremely brief. But surely our experiences doesn't seem to be composed of successions of brief spurts. Isn't it stream-like, flowing smoothly on for hours at a time? On this issue Strawson diverges from phenomenological orthodoxy. Describing the continuity – or lack thereof–to be found in his own experience, Strawson tells us that it is ‘continually starting or restarting … The basic experience, however much of it is smoothed out of attentional awareness in everyday life, is, I propose, one of tightly packed but non-seamless series of radically disjunct episodes.’ (238) Strawson concedes that many of us believe that our own streams of consciousness possess a far higher degree of continuity than this, but argues that this belief could well be false: we might be guilty of mistaking the continuities in the objects we perceive for continuities in the processes of consciousness itself. By way of further reinforcement, Strawson appropriates the ‘retentional’ approach to temporal awareness, as developed (in different forms) by Brentano, Husserl and C.D. Broad; on this model, the seemingly dynamic contents carried by individual specious presents are in fact packaged into discrete momentary episodes of experiencing, with the consequence that our streams of consciousness are composed of such episodes, in just the way Strawson himself proposes.

There are a number of considerations to bear in mind for those of us who find the Jamesian ‘stream’ metaphor more apt than inept. The retentional model may serve Strawson's purposes well, but so far as its originators were concerned it was fully compatible with the continuity of consciousness: Husserl himself subscribed to the view that consciousness is stream-like and experienced as such. That said, one of the criticisms laid at the door of the retentional approach is that it does lead to the fragmentation of consciousness, and for this reason is phenomenologically suspect, so Strawson may well deserve credit for appreciating – in a way that Husserl and his followers have not – the real consequences of adopting this conception of temporal awareness. But it doesn't really matter who is right with regard to this issue, because the retentional approach is by no means the only game in town. The main alternative is the ‘extensional’ approach advocated by Stern and Russell, and more recently by John Foster (and myself on several occasions). On this view, specious presents have genuine (objective) temporal extension, in just the way them seem to, and streams of consciousness are composed of overlapping series of these extended specious presents. Since this conception manifestly does not decompose streams into discrete momentary episodes, unless and until it can be shown to be flawed, the orthodox view of consciousness as continuous remains very much alive.

Although Strawson overlooks this alternative approach in his discussion of these issues, it is possible to anticipate at least one of the lines he would take against it. As a serious-minded materialist, Strawson is keen to develop ways of thinking about consciousness that are compatible with the scientific conception of the world; science, in the form of quantum theory, tells us that physical reality may itself well be radically discontinuous, at least on the smallest of time-scales, and the retentional model's discrete momentary episodes of experience are perfectly suited to a discrete or granular physical world – specious presents which are both continuous and temporally extended are not. But while we can all agree that fundamental physics is not to be taken lightly, it would surely be a mistake to assume that future (and better) physical theories will resemble, in all respects, our current theories–at the very least, let us wait for a viable quantum-gravity theory before drawing any firm conclusions. Also, and perhaps more importantly, with respect to this issue there is a serious tension in Strawson's own position. If our consciousness is as continuous as many of us believe, there is indeed a deep and difficult problem in reconciling this continuity with the micro-structure of the physical world. But this problem is by no means unique to the temporal features of our experience. How does the frenzied activity of the untold trillions of sub-atomic particles in my brain give rise to the spatially continuous phenomenal expanse that fills my visual field when I look up at a clear blue sky? This is a great mystery too, as most would acknowledge. Yet Strawson is more than willing to accept that our experience at a given moment is as unified and continuous as it seems to be. Indeed, he holds that the unity to be found in such experience is without compare. But if our experience can be unified in this way, despite any discontinuities at the level of elementary physical particles or fields, why not over brief temporal intervals? It is by no means clear that taking science seriously requires us to suppose that our streams of consciousness are less continuous than they appear to us to be, synchronically or diachronically.

So there are promising avenues to pursue for those who want to defend the continuity of consciousness against Strawson's assault. But if we follow Strawson in identifying selves with continuous stretches of experience, we are still going to be left with selves which last for at most a few hours – assuming, at least, that we lose consciousness as often as we seem to – which many will find unappealing. Here too, are a number of alternative paths worth pursuing, but I will mention just one.

Someone who believes that consciousness is a physical phenomenon, and who also believes that there is an intimate relationship between selves and consciousness but who isn't inclined to follow Strawson in equating selves with experience itself has a potentially appealing alternative: identify selves with (physical) systems that have the capacity to produce streams of consciousness, when appropriately stimulated, in the right sort of circumstances. Since these systems typically persist through periods of unconsciousness, the life spans of selves can extend beyond single streams of experience. Furthermore, since these neural systems are not themselves experiences the gap between selves construed as neural systems of this sort and experiences is sufficiently wide to allow us to say that selves have experiences (even if ‘having’ an experience amounts to producing experiences).

Strawson himself acknowledges the appeal of this approach early on, calling it the ‘brain-system’ view of the self: ‘It states that the self is whatever anterior-insula/precuneus/media-prefrontal-cortex/reticular-activating-system/etc. involving thing in the brain supports the consciousness and personality of a human being and is still there when the human being is in dreamless sleep. (10) And he goes on to register the appeal of the position: if you happen to be a materialist who favours a persisting self, ‘this is probably the view for you’. But he declines to take up the option himself. Why? On the grounds that it's part of his brief that the self must turn out to qualify as an object in fundamental metaphysics, the sort of metaphysics which is not in the least bit influenced by human schemes of categorization, but which reflects the real as it truly is. For Strawson, thin subjects have the advantage over brain-systems because they possess a high degree of unity, a form of unity that is without equal anywhere else. If, as Strawson urges, we take unity as the key criterion for distinguishing genuine objects from pseudo-objects, we can be sure that thin subjects will be counted as genuine objects in our most fundamental metaphysics. Only elementary physical particles–if there are any – and the universe as a whole, come remotely close to rivaling thin subjects when it comes to being entitled to object-hood. Or so Strawson argues.

I for one am more than willing to grant that the unity we find in our states and streams of consciousness is a genuine unity, even a remarkable one in some respects. I am less sanguine about Strawson's downgrading of the sort of unity that is to be found in complex material objects. Even if we leave their mental capabilities out of the picture, our brains are remarkable physical things, possessing as they do an incredible complexity and functional harmony. Brains may have the consistency of cold porridge, but their physical structure is very different – and very much more unified. Why should this remarkable degree of purely physical unity and organization count for so little in our fundamental metaphysics? As just noted, Strawson holds – plausibly enough – that the mark of fundamental metaphysics is its objectivity, its freedom from human bias. Arguably, in giving such weight to experiential unity, Strawson himself is guilty of imposing a very human perspective on the divisions to be found in fundamental reality.

Of course our brains – or more specifically our brain-systems – are remarkable in a further way: unlike lumps of cold porridge, they have the capacity to generate human streams of consciousness. Since we do not yet know how they manage to do this, it might turn out that this ability depends on a type or level of unity and organization in brain-systems about which we are entirely ignorant at present. In any event, the ability to produce and sustain human streams of consciousness is a noteworthy one in its own right, irrespective of whether it is associated with any additional physical integration. Furthermore, in so far as we are concerned with the correctness or otherwise of deeming brain-systems to be subjects of experience, the ability to sustain continuous streams of consciousness looks to be highly relevant – indeed, it is hard to think of what could be more relevant in this regard. But Strawson is unmoved:

Anyone who believes that subjects of experience can persist through periods of during which they are entirely unconscious is already, in effect, operating with a dispositional conception of subject-hood: they are subscribing to the view that subjects of experience are not always or essentially conscious, but rather, they are things that can be conscious. In this passage Strawson expresses a preference for an alternative, purely occurrent, conception: on this view, selves or subjects can only exist in conscious form. He is surely entitled to this preference, but it is not clear that he has given those of us who do not already share it sufficient reason to follow him in this regard.