Book Reviews are those electrical stimulations, given that they are the ones causing these experiences. So when the experience presents that there is a red, round object causing this very experience, then that experience is accurate: the thing normally causing this experience is in fact causing this experience of the thing, and is also presented as causing it. So it seems that intentional causation will not get Searle off the hook so easily. Some crucial claims in Searle's book thus appear in need of additional arguments to be fully convincing. However, it will certainly work as a provocative introduction to some of the philosophical problems of perception. Harmen Ghijsen Centre for Logic and Analytic Philosophy Institute of Philosophy, KU Leuven Andreas Vesaliusstraat 2 box 3220 3000 Leuven, Belgium Harmen.Ghijsen@hiw.kuleuven.be Semantic Externalism, by Jesper Kallestrup. London: Routledge, 2012, x+271 pages, ISBN 9780415449977 (pbk). As Kallestrup announces at the introduction of Semantic Externalism (2), the book examines the debate between semantic externalism and semantic internalism: is meaning wholly determined by internal features of the speaker (internalism) or is it at least partially determined by external such features (externalism)? Throughout the book's seven chapters the author presents and discusses a variety of interconnected topics in philosophy of language, mind and epistemology with the aim of arguing for semantic externalism. Two useful features of the book that make it a good introduction to the topic are that every chapter ends with a summary and annotated further readings. Another important feature is that the author critically assesses the main arguments for and against semantic externalism and semantic internalism; this allows the reader to have a proper understanding of the debate and of the metaphysical and epistemic implications of the conflicting theories. In short, the book offers an excellent description and an excellent introduction to one of the liveliest Book Reviews132 debates in contemporary philosophy. As semantic externalism is a reaction to Frege's and Russell's descriptive theories of names, the first chapter provides an introductory-level presentation of descriptivism. Without much discussion, but with sufficient detail, Kallestrup lays out some core concepts and distinctions which are a necessary basis to follow through the whole debate. What referring terms are, what is specific of their types, in what respects the semantics of these terms differs from that of predicates and sentences, what compositionality and substitutivity concerning reference is, are some of the topics addressed. Descriptivism is presented as both a theory of meaning and a theory of reference. As the first, it states that the meaning of referring terms is given by definite descriptions, as the latter, it claims that objects are referred by terms associated with most of descriptions in a cluster (Searle's "cluster theory"). Besides offering a brief presentation of descriptivism, Kallestrup also discusses whether Frege's identity argument - a.k.a. Frege's puzzle - supports descriptivism. A point worth mentioning in more detail is his thoughts on the relation between communication and Frege's notion of sense. The worry is that communication is at risk if senses determine meaning, for even though they are universal, they are also not necessarily shared. Frege did not give much thought to the problem, saying that as long as people shared the same sense, we could tolerate it (did he meant that communication would be assured?). Still, Kallestrup argues that sharing senses is not enough, because sometimes speakers also need to know that they share them. His counterexample involves two speakers co-identifying a man with the description 'a very drunk American in the Cellar Bar last night', and both naming him 'Jack' without knowing the other has done the same. When, on a later occasion, one tells the other 'Jack got thrown out', even if the second rightly believes that the man he calls Jack got thrown out of the Cellar Bar, Kallestrup claims that they did not communicate that Jack got thrown out of the Cellar Bar, because they did not know that they both use 'Jack' to refer to the same person. His diagnostic is that: Only by chance do we end up thinking about the same man in the same way. For all I can tell, 'Jack' in your mouth picks out the quiet Scotsman in the Cellar Bar last night. Such luck excludes knowledge of what you said. 133Book Reviews So, there are cases in which understanding requires not only that speakers think of objects in similar ways, but also know that they do. (31-2) We think otherwise. Firstly, the requirement that speakers know that they are thinking of objects in similar ways does not seem necessary for communication to occur. It is too strong. Something weaker like speakers believing that they are thinking of objects in similar ways seems to us a more promising candidate as a requirement for understanding. Secondly, if we doubt that 'Jack' in your mouth means the same man we mean by 'Jack', then we do not believe that that Jack was thrown out. Why would we? If we are competent users of the language, then, unless we have some appropriate false beliefs (e.g. that speakers do not use the same name for different persons), we would immediately ask 'Which Jack are you talking about?' But then, after disambiguation, the counterexample is gone because our exchange would not be based on chance any more. As Recanati reminds us [...] we keep monitoring each other's understanding of what we are saying, making repairs when necessary, negociating meaning, etc. [...] the interactive nature of mutual understanding in communication is what ensures convergence and content-sharing (Recanati, F. 2011. Truth-conditional Pragmatics. Oxford University Press: Oxford, p. 8). Without accepting this, Kallestrup falls victim to his own criticism of Frege, for he would also say we misdescribe much of our daily conversations as communication. Moreover, it is unclear in what way is this a specific problem for descriptivism. The next chapter deals with an alternative to descriptivism: referentialism. Contrary to what he does in the previous chapter about descriptivism, here Kallestrup presupposes some familiarity with the theoretical background. For instance, while distinguishing rigid designation from direct reference, the distinction between de jure rigidity (said to pertain directly to referential terms) and de facto rigidity (said to pertain to some descriptions) deserves little attention. Yet, this distinction plays an important role in Kripke's widely accepted criticism of descriptivism. Nonetheless, this chapter provides a good outlook on referentialism, focusing on Kripke's famous modal argument but also considering with some detail the descriptivist wide/ narrow scope reply. Kallestrup presents this particular discussion between referentialists and descriptivists in an accessible way. Book Reviews134 Chapter 3 connects the debate in philosophy of language between descriptivism and referentialism with the more general debate between semantic internalism and semantic externalism. The main point here is to provide further arguments against descriptivism, by arguing against semantic internalism. Hence, Putnam's Twin Earth and Burge's arthritis arguments are discussed. As a challenge to historical externalism, Davidson's Swampman argument is also considered in detail. At this point we have one remark regarding Kallestrup's characterization of externalism. To go into this let us start by remembering briefly Putnam's argument. Putnam asks us to imagine a twin earth where everything is exactly the same as our earth, except that water in twin earth is not H2O, but XYZ. Now, when Mary and twinMary use the term 'water' they are not referring to the same thing (twin-Mary refers to XYZ and Mary refers to H2O). Although they share psychological states (including those about water), their use of 'water' is not co-referential. Thus, 'water' in twin earth and 'water' in earth differ in meaning. Putnam's conclusion is that psychological states are insufficient to determine meaning, and this undermines descriptivism since it is committed to semantic internalism. Kallestrup then goes on to explain what semantic externalism is: [propositional] content is in part determined or individuated by features external to the individuals who are in states with that content, i.e. that such content supervenes on the conjunction of internal features (intrinsic physical, experiential, psychological properties) and external features (62). However, we think that this characterization excludes versions of externalism which admit that external features alone can determine meaning. A more precise characterization would say that propositional content is at least in part determined by external features. Since Kallestrup himself offers this characterization at the introduction (2), this is probably an unintended omission. However, the reader could be puzzled by such disparity. Kallestrup also considers some internalist replies to the Twin Earth argument. The most prominent is perhaps the one that takes the natural kind term 'water' to have an indexical element. According to this solution, 'water' expresses the concept the watery stuff of our acquaintance. Kallestrup responds by claiming that such 135Book Reviews solution fails to establish the existence of narrow content (67). If this is right, then the reply fails to salvage the claim that the difference in content comes down to an internal difference. Chapter 4 focuses on the distinction between narrow content and wide content. This is important because both Burge's and Putnam's arguments in the previous chapter purport to show that (most) mental content is wide, not narrow - it is not determined by its intrinsic properties. However, these arguments fail to show that mental content is wide "in circumstances in which (...) facts [related to such content] are absent" (122). This is why Boghossian's Dry Earth argument is examined in detail. The upshot of the argument is that semantic externalists are committed to the claim "that Dry Earthlings express no concept by 'water'" (123). Boghossian's Dry Earth argument shows that one needs to assess the different ways that narrow and wide content "hook on to the world" (122). This means that semantic externalism also has metaphysical consequences and that it can also be characterized as a metaphysical thesis: "representational states such as beliefs depend for their individuation on features of the external physical, historical or sociolinguistic environment" (117-8). Thus, an important issue to be addressed is how narrow and wide content relate to the external world. For the case of narrow content, Kallestrup argues that it should not be construed out of intrinsic properties. The reason is straightforward: "narrow content determines what (...) [is picked] out if the environment is so-and-so" (122); therefore, it should be modelled on dispositional properties instead. The following two chapters are no longer focused on language and mind, but on the putative epistemic implications of semantic externalism, mainly, its incompatibility with self-knowledge, on chapter 5, and its too-good-to-be-true denial of external world scepticism, on chapter 6. After a fairly general introduction to self-knowledge, much of chapter 5 rests on Burge's epistemology and his specific view on selfknowledge. For Burge there are two kinds of warrant: entitlements, which are epistemically externalist, and justification, which is epistemically internalist. On his view, just as perceptual beliefs may be warranted for a subject S without S being able to justify them, the same happens with self-knowledge. Both are entitlements, but while Book Reviews136 self-knowledge is warranted a priori, perceptual beliefs are warranted a posteriori. But simultaneously accepting self-knowledge and semantic externalism brings about the worry of incompatibilism, that is, the view that semantic externalism is incompatible with self-knowledge. Building on Burge's self-verifying judgements (second order necessarily true thoughts like Descartes' cogito), Kallestrup's conclusion here is that "external individuation does not all by itself give rise to additional difficulties in explaining how we can have privileged knowledge of our own minds" (143). Once we accept semantic externalism it appears pretty straightforward to accept that "[...] if our thoughts have their contents in virtue of our standing in certain relations to our external environment, then introspective knowledge of those contents can afford us similar knowledge of relevant environmental features" (162). This relates knowledge about our mental contents (discussed in the previous chapter) with knowledge about the external world. Thus, semantic externalism has the tools to argue against external world scepticism by claiming that we can come to know environmental features via introspection. The immediate concern here is that semantic externalism may imply "an a priori route to specific, empirical features of the external world" (163) and such consequence is undesirable. On the other hand, if it is not so, semantic externalism is seemingly ill-equipped to deal with the sceptical challenges concerning knowledge about the external world. Chapter 6 deals with such issues and challenges. Since most sceptical arguments rely on the principle that "knowledge is closed under known entailment" (158) - or closure - Kallestrup rejects it. We cannot review here all his arguments for its rejection, but we find one of them particularly interesting. The argument rests on Nozick's sensitivity requirement for knowledge: "S knows that p only if: were p false S would not believe that p" (165). Now assuming that p is S is not a brain in a vat (BIV), then the requirement above fails because S would still believe that p, that is, that she was not a BIV, when she is in fact a BIV (according to the standard BIV story). Yet, continues Kallestrup, the requirement is satisfied when p is S has hands for "in the closest possible worlds in which S does not have hands, she has stumps (or something similar), and so in those worlds 137Book Reviews S does not believe that she has hands" (165). Furthermore, she also knows that if she has hands then she is not a BIV. So, having the antecedent of this conditional, together with S's not knowing that she is not a BIV, is all it takes for closure to fail. If this is right, the BIV sceptical scenario does not show that we cannot know that we have hands. Instead, together with Nozick's sensitivity requirement it implies that closure is not universally true. Chapter 7 offers the reader a tour on the metaphysical implications of semantic externalism, specifically implications that regard mental causation. Here Kallestrup provides various reasons to consider the following varieties of mental causation: physical to mental causation; mental to mental causation; and mental to physical causation. Two main problems with mental causation are afterwards mentioned: (i) "how mental states qua mental can cause something physical" and (ii) "how mental states qua contentful can cause something physical" (188). While problem (i) is that mental causation threatens the causal closure of the world, problem (ii) is that content seems causally irrelevant and this is a challenge for semantic externalism. Chapter 7 deals in great detail with the different strategies that semantic externalism may use to answer problem (ii). Semantic Externalism is a great book for anyone who wishes to dwell on the semantic externalism/semantic internalism debate. In addition, owing to the intersection of topics it concerns, the reader is offered a discussion of many famous arguments that he or she would otherwise only get in more than a single book. Ricardo Miguel LanCog Group Centro de Filosofia da Universidade de Lisboa Alameda da Universidade, Campo Grande 1600-214 Lisboa Portugal ricardomiguel@campus.ul.pt Diogo Santos LanCog Group Centro de Filosofia da Universidade de Lisboa Alameda da Universidade, Campo Grande 1600-214 Lisboa Portugal diogoferreirasantos@campus.ul.pt