This is a big book. Stretching to over 500 densely printed pages, its heft is matched by its ambition and erudition. The book's central theses are two: ‘The Reasons thesis’, the view that ‘the concept of a reason is the fundamental normative concept’ (p. 77); and ‘Cognitive irrealism’, the view that propositions about reasons can be true and, when true, are knowable a priori; but that they are not made true by any ‘substantial’ fact – a fact that has an essence or constitution and that can ‘cause and/or be caused’ (p. 404) – to which the true proposition corresponds. There are facts about reasons only in the ‘nominal’ sense that there are true propositions about reasons, where a ‘proposition’ is ‘the sense or meaning of what is asserted on an occasion’ (p. 403). According to Skorupski, defending these two theses amounts to defending a new version of a ‘Critical’ philosophy in the broad Kantian sense of a philosophy that, as against both scepticism and dogmatism, explains how much of our ‘common cognition’ (p. 6) can amount to knowledge; and that explains how self-determined action – and, in a striking disagreement with Kant, also self-determined feeling – is possible. The result is nothing less than a comprehensive new theory of the ‘relation between self, thought, and world’ (p. 1). This is heady stuff indeed, but Skorupski navigates a complex and difficult terrain with enviable grace. His discussion is peppered with instructive historical commentary while maintaining focus on argumentation engaged with contemporary concerns. There are helpful examples galore. While this is not a racy read – what 500-page volume of contemporary philosophy is? – it is never boring and always worthwhile.

I will first outline how the edifice is built, and then provide some critical commentary. Start with the Reasons thesis. It says that ‘the concept of a reason is the fundamental normative concept’, in the sense that ‘the sole normative ingredient in all normative concepts is the concept of a reason’ (pp. 77–8). ‘Normative’ concepts for Skorupski include both evaluative concepts like the concept of a person's good, as well as deontic concepts like the concept of moral wrongness. Moreover, not just practical norms governing action, but also epistemic norms governing belief, and what Skorupski calls ‘evaluative’ norms governing feeling, are all ultimately propositions about (practical, epistemic, or evaluative) reasons. Indeed, for Skorupski, all synthetic a priori propositions – including, for instance, propositions about aprioricity, necessity, probability, and evidence – are ultimately normative, and so about reasons; or else are non-normative ‘offshoots’ of propositions about reasons. The domain of reasons, or of propositions about reasons, is thus larger than one might have initially thought. The task of providing such ‘buck-passing’ analyses of a wide range of concepts in terms of the concept of a reason occupies much of the book (parts II and III, as well as some sections of part I).

How does this get us closer to a comprehensive picture of ‘the relation between self, thought, and world’ (p. 1)? The key to Skorupski's overarching Critical enterprise is the claim that we can have a priori knowledge of normative truths (i.e., given the Reasons thesis, of truths about reason relations); and that both self-determined action, feeling and belief, as well as knowledge of ordinary non-normative facts, are made possible by, and require, this a priori normative knowledge (pp. 19–27, 477–8). Because a priori knowledge cannot be of ‘substantial’ facts (sections 6.2–6.3), it must be of ‘nominal’ facts. This recommends Cognitive irrealism about reason relations. As to how we can know nominal normative facts a priori, Skorupski's answer is: through the exercise of ‘spontaneous normative dispositions’ and the correction of their deliverances through ‘dialogue’ with others (ch. 16). The crucial argument that self-determination and knowledge of ‘substantial’ facts hinge on a priori normative knowledge involves subtle issues about the nature of knowledge in general, of self-determination as a kind of responsiveness to reasons, and indeed of the ‘world’ as an object of knowledge. For instance, on this last score, it turns out that what we might have thought were wholly substantial knowable facts are partly substantial, but partly normative and thus partly nominal (p. 501). I will not broach these thorny issues here; some of them have been discussed in other reviews. (For Skorupski's discussion of them, see esp. sections 1.5–1.6 and 3.1, and chs. 5–6, 10 and 19–20.) Instead I focus in the remainder of this review on the claim that all normative and evaluative concepts can be analysed in terms of the concept of a reason for some response.

Take the concept of a person's good – a concept that is by Skorupski's own admission central to ethics. Skorupski holds that ‘a state of affairs is part of a person's good if and only if there is reason for this person to desire [t]hat it obtains’, ‘or would be . . . reason for [the person] to desire [that it obtains] if [this person] were capable of sufficiently developed desires’ (pp. 267, 85). This is a ‘sentimentalist’ analysis of (the concept of) a person's good, in the sense that the notion of desire to which it appeals ‘should be placed with the feelings, not with the will’ (pp. 268, 239–41): a person's good is analysed in terms of reasons for a kind of affective state.

The primary concern I have about this analysis is that it seems false that everything there is reason for a person P to desire is part of P's own good. For instance, there seem to be reasons to desire not just what is good for oneself but also what is good for others, good for the planet, or perhaps just a good state of affairs. Skorupski tries to address this concern, arguing that a person's good can expand to encompass (e.g.) the good of others. If I care sufficiently about these others, ‘identifying’ with them, then their faring well is plausibly also part of my own good (pp. 278–80). In response, however, while it is plausible that a person's good can so expand, this doesn't address the concern that there may also be cases in which a person's good hasn't so expanded. Suppose I don't identify with certain others, or desire their good. It seems that there might nonetheless be good reason for me to desire their good. Skorupski doesn't explain why, in such cases, we should think that those others’ good is also part of mine.

Skorupski claims, however, that the ethical point of the notion of a person's good counts in favour of his analysis. Since ‘a wide range of ethical positions’ hold that a person's good is something we should take account of, then if a person's good diverges from what that person has reason to desire, the question arises as to which of these we should take into account, and in what way:

I am unconvinced. The first option Skorupski considers in the quote above is a red herring. We needn't deny that outcomes that promote P's good are outcomes that P has reason to desire, in order to hold that P may also have reasons to desire outcomes other than P's own good. Regarding the second option, suppose that what P has reason to desire diverges from – is more expansive than – P's own good. Skorupski's concern seems to be that there is then no way to decide whether to take into account P's good or what P has reason to desire – and in particular, no way to ensure that P's good has the ethical significance it seems to have. However, surely we can grant that P's good matters ethically – as does the good of every person – even while granting that other things P has reason to desire might matter too (such as the good of other people, or perhaps the freedom to live by her own autonomous choices, even if the upshot of these choices diverges from her good). It's true that it's not obvious how to balance these and other issues in many ethical contexts. But crucially, this is a question for substantive normative ethical reflection, and isn't plausibly something to be decided by an account of the very concept of a person's good.

Suppose we reject Skorupski's analysis of the concept of a person's good. It's not clear how to provide a better buck-passing analysis. One might suggest that P's good is that which P, or perhaps anyone, has reason to desire for P's own sake. But, as Skorupski notes, here the concern arises that the notion of desiring something ‘for P's sake’ cannot be accounted for without appeal to the notion of P's good (p. 285). (For a recent article that is sceptical of the general prospects for buck-passing analyses of a person's good, see Guy Fletcher's (2012) Philosophical Studies piece ‘Resisting Buck-Passing Accounts of Prudential Value’.)

How bad would it be for Skorupski's overall Critical project if not every normative or evaluative concept could be analysed in buck-passing terms? Skorupski himself sometimes suggests that there might in principle be alternative ways to ‘inter-define the circle of normative concepts’ (pp. 77, 481). And he is happy to accept an ‘irreducible trichotomy’ of epistemic, practical and evaluative reasons (section 2.9). So why worry if it turned out that there were no unitary analysis, but simply some irreducible value concepts, some irreducible reason concepts, and perhaps more besides? This depends in part on whether Skorupski's normative epistemology can be extended to account for knowledge of value even if the relevant value doesn't allow for a buck-passing analysis. Unless Skorupski's epistemology can be so extended, his Critical picture of the ‘relation between self, thought and world’ must disappointingly leave out of account knowledge of, and appropriate responsiveness to, some important kinds of value. Still, knowledge of non-normative facts might remain in place if Skorupski's buck-passing analyses of epistemic notions stand. Nor is it clear that Skorupski's view of self-determination would be fundamentally affected (for some relevant discussion, see section 12.4).

I haven't been able to say anything about Skorupski's illuminating analysis of moral wrongness in terms of reasons for the sentiment of blame; about his analysis of rights in terms of moral permissibility, or justice in terms of rights (ch. 12); or about his analyses of impartial principles of ‘good’ and ‘demand’ in terms of agents’ reasons for action (chs. 13–14). The same goes for many other topics. The sheer breadth and depth of The Domain of Reasons is dizzying. But the tome amply rewards careful study, and I know I will be returning to it in the months and years to come.