The Wonder of Consciousness: Understanding the Mind through Philosophical Reflection by HAROLD LANGSAM. (The MIT Press, 2011. Pp. x + 234, Price £24.95 cloth.) Harold Langsam thinks that consciousness is a wonderful thing, and he wants to articulate what that wonder consists in. To do so, he puts his cards on the table early on. If you don't already share most of Langsam's commitments then you'll need to entertain them for the duration. This might be a stumbling block if you share very few of them, so here's a list: Rationalism: a priori knowledge is possible, un-mysterious, and relatively abundant. (7) Essentialism: metaphysical categories like properties and universals have intrinsic features which make them what they are, and which account for the existence of necessary relations between them (8). Nonreductionism about mental states and mental properties: "... mental properties are neither structural physical properties nor causal properties that are realized by physical properties. In other words, mind is different from body." (18) Authority of introspection: introspection is a 'direct' and dominant source of evidence about lots of things, but in particular about the (intrinsic) properties of conscious mental states (19-21). Primitivism: the intrinsic natures of the phenomenal characters of experiences are sui generis and inexpressible. Folk-psychological realism: terms like 'belief', 'desire' and 'knowledge' refer to propositional attitudes, which are psychologically real categories of mental states. There are several passages early on which purport to show that the various theses are consistent and mutually supporting. If you're suspicious about all of them, well, Langsam's probably not writing for you. At various points he tells us that he thinks arguing over these positions is a distraction – that he 'knows of no serious philosophical arguments that purport to show' that a priori knowledge isn't possible, that there aren't necessary relations between distinct properties, or that introspection could be defeated by argument. Engaging with these debates would be to engage with philosophers who are ignorant, misled, deluded or hypocritical about the nature of philosophy. The book's main thesis is that consciousness (exemplified by perceptual experiences and their associated phenomenological properties) is wonderful – which is to say: philosophically interesting – because it is one of a few domains in which we can acquire something like synthetic a priori knowledge. Langsam argues that by reflecting on our conscious experiences of the world, and on those of their properties which are available to introspection, we can learn about lots of relations which do or do not hold between them. In so doing, we come to grasp truths about these 'intelligible' relations (they are 'intelligible relations' because they are available to reflection). The fact that we can grasp such truths just by this process of reflecting on our perceptual experiences is, in Langsam's terminology, wonderful: it demonstrates that there are intelligible relations there for the grasping. By a priori reflection, we come to know truths about relations between the mind and world. This thesis – the wonder of consciousness – appears at the start and at the end, but drives the central chapters of the book, which concern perceptual experience and phenomenal properties, mental causation, the rationality of beliefs, and the appropriateness (or otherwise) of some desires and their objects. The notion of 'consciousness' involved is not explicitly theorized; this isn't a monograph about higher-order thought theories or the kinds of things that might appear in a philosophy of psychology volume. Nor is the (rather crucial) notion of 'reflection' investigated: Langsam takes it as given that we know reflection when we're doing it. In most cases the mere fact that we can reflect on possible interrelations between our experiences and their phenomenal properties, or between pleasurable sensations and our desires for them, is taken to be sufficient for showing that there exists intelligible relations between them. He doesn't provide further explanation of what he thinks the mechanism is that enables or facilitates our ability to get to know about these intrinsic natures which, in turn, enable us to acquire a reflective grasp of the relevant properties. Rather, the arguments proceed by suggesting that we can reflect on certain features of our mental lives, and that since we can, there must be some sort of intrinsic something that enables this to happen. So a couple of questions stand out: for starters, what is this link between reflection and intrinsic properties? Assuming that 'to reflect' is just to have thoughts about something, it's not at all clear that Langsam's account of the mere fact that I can think about something helps to elucidate how I end up learning anything more substantial than that very (mere) fact: that I can have those thoughts. When I have a conscious thought about the house-move I might conduct in the following weeks, I might go through a range of other thoughts (Have I budgeted to afford the deposit as well as the van hire? Can I lift the sofa by myself? Is there anything more to my life beyond constantly moving house?). From these thoughts I might be tempted to think or suppose that my possible future house-move thoughts have a range of properties – perhaps they're insignificant properties, but they're intelligible properties nonethe-less. Whether we should reify such properties isn't questioned: that we can think about them shows that there are such properties. And when I think about those properties, I can reflect on how they're related to each other, and so establish their intelligible relations. It's not clear that I've learnt very much in the process, unless we also suppose (reifying again) that there's something like a bunch of causally efficacious and intelligible intrinsic properties of the future house-move thoughts that give rise to these relations and enable me to do this all thinking. If there must have been, then we've learnt something which looks a bit more philosophically substantial: that my future house-move thoughts have intrinsic properties. Is this an abductive argument? Or an indispensability argument? Or a transcendental argument? It certainly seems to be a little worryingly thin: we postulate the existence of these intrinsic properties of future-house move thoughts, and at the end we learn that we've learnt something wonderful (intelligible) about those house-move thoughts, vis. that they have these intelligible intrinsic properties which stand in these intelligible relations. Whether this is a decent way to acquire knowledge of the intrinsic properties of thoughts, should any of either exist, depends on what kind of argument it is; the propriety of abductive inferences, indispensability arguments and transcendental manoeuvres are much discussed, but not here. The second issue also concerns reflection: is it informative or reliable? Take the analogy with introspection: Langsam thinks that introspection gives us a posteriori evidence that reductionism is false. He also thinks that it's obvious (upon reflection) that we should never let our introspections be overturned by argument. But while most post-Cartesian philosophers might be prepared to countenance the thought that introspection is a defeasible source of evidence – that even if it's reliable (and that's questioned too) it rarely delivers certainty – the issue never comes up with Langsam. There are various options to play with here; for example, Fiona MacPherson recently defended a disjunctivist theory of introspection on states involving phenomenal characters. But just as Langsam doesn't seem to question the certainty of introspection, so similarly he doesn't address the defeasibility of reflection, and in lacking a worked-out account of that, his repeated claims about the intelligibility or 'wonder' of consciousness are less wondrous. JOE MORRISON Queen's University Belfast