Reason and Explanation: A Defense of Explanatory Coherentism. BY TED POSTON (Basingstoke, UK: Palgrave Macmillan, 2014. Pp. 208. Price £ 60.) In this interesting book, Ted Poston delivers an original and powerful defence of explanatory coherentism about justification. Let me summarize the very rich contents of its seven chapters and emphasize some points of strength and weakness. The introduction starts with a lucid synopsis of recent history of coherentism (from Otto Neurath to contemporary Bayesian coherentists), followed by responses to the input and the alternative system objections, which are standardly raised against coherentism. Poston's reply to the first objection exposes an important feature of the original type of coherentism that he defends. The input objection says that coherentism is implausible because coherence sets no justifying role for experiences. Against this, Poston proposes that the experiences a subject S, conceived of as states with representational contents, can contribute to the justification of S's overall belief system in virtue of the coherence between the contents of S's experiences and the contents of S's beliefs. Coherence is, on Poston's view, a relation holding between the contents of, indifferently, nondoxastic and doxastic assertive states. This view would enable experiences to be necessary (but not sufficient) to justify beliefs of certain types. Although this response to the input objection looks promising, my impression is that it remains insufficiently detailed in the book to actually permit an assessment of it. The second chapter defends epistemic conservatism, which is a key ingredient of Poston's coherentism. According to epistemic conservatism, the mere attitude of believing P generates some epistemic justification for the belief that P. Poston defends an original variant of it according to which whenever S believes P in a situation of empty symmetric evidence (i.e. whenever S lacks any evidence for P and Not-P), S has some justification for her belief. Empty symmetric evidence characterizes––according to Poston––our epistemic predicament with respect to the hinge 2 propositions that are at the basis of our cognitive projects and must be part of any coherent belief system. (Propositions of this type state, for instance, that memory is normally reliable, that certain inferences are truth-conducive, and that meaning is stable.) In Poston's picture, hinge propositions receive some initial justification just in virtue of being believed by us and independently of coherence itself. According to Poston, this enables coherentism to escape a pernicious form of circularity that afflicts Laurence Bonjour's formulation of it. Poston argues that epistemic conservatism doesn't conflict with the ultimate epistemic goal of believing all and only truths. Most of this chapter addresses well-known objections to epistemic conservatism (e.g. David Christensen's and Richard Foley's). Poston's responses struck me as persuasive in many cases. Epistemic conservatism is claimed to be vindicated by the perspectival nature of epistemic internalism, which involves that we cannot but rely on antecedent beliefs about what counts as good sources of justification to determine what beliefs are justified. The third chapter details a coherentist account of reasons for believing. Poston puts forward fresh arguments and re-proposes classical cases for denying the existence of basic reasons––i.e. propositions that work as regress-stoppers because they are non-inferentially justified and capable of supplying inferential justification for believing other propositions. An argument against noninferential justification revived by Poston is Sellars dilemma, which assumes that experiences with representational contents can justify beliefs only if there is independent justification for taking the contents to be accurate. I was disappointed to observe that influential views like phenomenal conservatism and dogmatism, which reject this assumption, aren't explicitly countered by Poston. Another battery of arguments targets the thesis––which Poston attributes to the foundationalist–– that basic reasons enable direct ampliative inferences; namely, ampliative inferences resting on no background assumption. Poston contends that any good ampliative inference must rest on some explanatory background assumption. Drawing from these arguments, the chapter articulates and defends a neat account of reasons to the effect that a proposition is a reason for believing another 3 proposition only within a coherent framework of beliefs. Precisely, P is a reason for believing Q for S at t if and only if (i) S is justified in believing P at t; (ii) P is insufficient for Q's justification; (iii) P is a non-redundant part of some larger set of propositions that are unnecessary but sufficient for Q's justification; and (iv) S is justified in believing at least one of those larger sets of propositions at t. The fourth chapter aims to clarify the link between explanation and justification within an overall coherentist picture. Poston maintains that we use explanations to remove mysteries but contends that explanation is an unanalysable relation between propositions. The chapter delivers a few, quite convincing cases for this conclusion. Poston argues that explanation is a cognitive virtue because epistemic agents aim at believing truths that produce understanding. The constituents of the virtue of explanation are claimed to be conservativeness, explanatory power and explanatory simplicity––the chapter illuminates the last two. Poston defends the view that S is epistemically justified in believing P as long as P is part of a conservative, simple and powerful explanation that beats all rival explanations conceivable by S. This holistic conception of justification is in turn vindicated by an argument to the best explanation of our epistemic practices and intuitions about epistemic notions. Poston's explanationist coherentism is claimed to be a variant of the internalist, mentalist and evidentialist conception of justification. The fifth chapter defends some of Bonjour's earlier anti-foundationalist /coherentist theses form Bonjour's recent anti-coherentist/foundationalist arguments. Poston substantially intends to show that Bonjour's recent attempt to resolve Sellars dilemma in favour of foundationalism fails because it conflicts with the perspectival nature of internalist epistemic reasons. The chapter begins with an illuminating presentation of Bonjour's earlier anti-foundationalist argument according to which there cannot be basic empirical beliefs. The presentation uncovers the reliance of Bonjour's argument on Sellars dilemma and Bonjour's criticism of C.I. Lewis' doctrine of the given. Poston then scrutinizes and rejects Bonjour's recent case for the existence of basic beliefs grounded in the 4 thesis that non-conceptual and non-propositional experiences can give us reasons to believe certain propositions. A similar argument by David Chalmers is analysed and rejected. This strikes me as one of the most insightful chapters of the book. The sixth chapter targets Bonjour's foundationalist account of a priori justification. Poston argues that Bonjour's reasons to believe that certain propositions and principles of reasoning are justified a priori by an autonomous rational faculty are at best inconclusive, for an equally plausible but fully coherentist account of the justification of these propositions and principles can be provided. Poston also endeavours to defuse Bonjour's contention that explanatory coherentism cannot justify the principle of non-contradiction on pain of conceptual incoherence and epistemic circularity. Some of Poston's arguments strike me for their originality and perceptiveness. Poston finally contends that the subject need not be aware that her belief system is coherent to have justification for it. This defuses another important anti-coherentist challenge made by Bonjour. The last chapter investigates whether explanatory coherentism fits into Bayesianism. In effect Poston essentially addresses Bas Van Fraassen's controversial argument that Bayesianism and inference to the best explanation are incompatible. (I was surprised to find out that the important "impossibility results" of Bayesian coherentism, according to which there is no Bayesian measure of coherence that makes coherence truth-conducive, aren't analysed in the book.) The chapter begins with an excellent overview of Bayesianism followed by a presentation of Van Fraassen's incompatibility argument. Drawing from work by Peter Lipton and others scholars, Poston questions the incompatibility argument and defends an original view according to which explanationism and Bayesianism are compatible because, for the purpose of obtaining inductionfriendly probability functions, the subject's prior probabilities distributions need to reflect explanatory virtues. 5 As this outline shows, this work isn't an introduction to coherentism but, rather, an inspiring monograph that actually advances research in this field. Scholars and postgraduates interested in the recent debate on coherentism about epistemic justification should definitely read this book. University of Aberdeen LUCA MORETTI