Christopher Peacocke: The Realm of Reason Oxford University Press U.K. 2003 0–19–927072–4 Hb £25.00 x + 284 Julian Fink Corpus Christi College, Oxford By applying our capacity to reason, we unavoidably make transitions from one mental state to another: from "p and q" is true we infer that p is true; from perceiving a tree with green leaves we judge "this tree has green leaves"; from the fact that all perceived trees have green leaves, we gather that "all trees have green leaves"; and from our moral intuition that one ought to help those, who cannot help themselves, we are led to the belief "I should help the blind woman crossing the street". Some of these transitions will be rational, some not. For those transitions which are rational, there must be reasons explaining their rationality. These reasons will entail why and when a thinker is entitled to make a transition. In his recent book The Realm of Reason, Christopher Peacocke's presents a rationalist theory defining when a thinker is entitled to make a transition from one set of mental states to another. Peacocke conceives this book as part of a trilogy: In A Study of Concepts (Cambridge, Mass.: MIT Press, 1992), he argued that reference and truthconditions play a key role in determining the possession-conditions for concepts. In Being Known (Oxford: OUP, 1999) he examined the relation between truth and knowability in light of his possession-condition theory for concepts. In The Realm of Reason, Peacocke combines his earlier efforts. By bringing together his theory of concept-possession, truth and knowability, he establishes a general theory of entitlement to mental states. Peacocke's theory is distinctively rationalist. He claims that if a thinker is entitled to a transition from one set of mental states to another then (at least) part of this entitlement will be given independently of experience and thus will be a priori. Peacocke's approach goes beyond traditional accounts of entitlement. Leibniz, Frege or Gödel, for instance, are chiefly concerned with the idea of how we are entitled to outright a priori truths ("it is impossible for p to be and not to be the case") without relying on sense experience. Peacocke's rationalism, however, is more ambitious. He attempts to set forth a generalised rationalism which defines one entitlement condition to fit all possible kinds of transitions between mental states. Peacocke's entitlement condition implies that any transition to which a thinker is entitled is fundamentally a priori. Peacocke develops his argument by setting out three principles of rationalism. This gradual presentation makes it easy to follow the structure of his thesis. This said, Peacocke keeps the discussion of the individual principles at a sophisticated level by drawing on a large number of sources and concepts. Whilst this may boost the depth of his analysis, it makes it difficult for those who are new to the field to follow the discussion. In addition, Peacocke does not hesitate to employ philosophical jargon which sometimes remains to be suitably explained. Peacocke's first principle of rationalism-"The Special Truth-Conduciveness Thesis"-argues for a strong connection between entitlement and truth: A fundamental and irreducible part of what makes a transition one to which a thinker is entitled is that the transition tends to lead to true judgements (or, in case the transition relies on premises, tends to do so when its premises are true) in a distinctive way characteristic of rational transitions. (p. 11) In short, "[r]ational ways of coming to make judgements must be ones that tend to lead to the truth" (p.13). In order to support the importance of truth in defining entitlement, Peacocke insists that there is no arguable alternative which could define the conditions for entitlement to judge that "p is F" without making reference to the truth-conditions of when p being F is true (p. 22, cf. pp. 15-23) Taking for granted that truth plays a significant role in justifying a judgement, it seems legitimate to ask whether Peacocke is right in his claim that truth is the only plausible criterion of justification. Pragmatists, for instance, argue that not only content related reasons, but also other, i.e. "pragmatic" reasons can justify judgements. Suppose you have no reason to believe that there is no mafia in Sicily. The evidence you perceive speaks strongly against it. Yet being Sicilian you may have a reason to hold this belief. It simply makes your life go better. Although this belief might lack an epistemic justification, it still seems rational under some description. Therefore, it seems conceivable to allow a more pluralistic account of justification, accepting various sources of cognitive entitlement. Whereas Peacocke's first principle could be a component of a non-rationalist theory of entitlement, Peacock's second principle, "The Rationalist Dependency Thesis", is distinctively rationalist: The rational truth-conduciveness of any given transition to which a thinker is entitled is to be philosophically explained in terms of the nature of the intentional contents and states involved in the transition. (p.52) Peacocke's second principle goes far beyond the classical canons of rationalism (cf. pp. 52-60). Classical rationalists are concerned with how reason entitles us to take a priori contents as knowledge without relying on sense-experience or perceptual content (p. 52). For Peacocke, however, entitlement concerns all "content-endorsing transitions" (p. 59; Peacocke's emphasis), including transitions from perceptual experience to perceptual judgment. According to "The Rationalist Dependency Thesis" the fact that such transitions are truth-conducive must be explained by the nature of the contents and states involved in the transitions. For judgements based on our perceptual experience this explanation has two aspects: (i) to show that the content of our perceptions represents the world truthfully and, if so, (ii) the transition from a perceived content to a demonstrative judgement preserves the truth of the perceptual content. This raises the question of why the credibility of our perceptions and their resulting judgments are not undermined by the possibility of sceptical hypotheses which deny that perceptual content represents the world truthfully. To abandon scepticism as a barrier for perceptual entitlement, Peacocke argues that the assumptions of sceptical hypotheses are unwarranted. Peacocke's argument against sceptical hypotheses concentrates on a positive correlation between the truth of a hypothesis and whether it reduces complexity. Peacocke argues that the fact a theory reduces complexity "counts in favour of its confirmation, because it is an explanation that does not make it hard or excessively improbable for the postulated explaining condition to be true" (p. 97). Peacocke claims that the only complexity reducing theory available to us explains the emergence of perception through a natural selection process, aiming to enhance our chances to survive. Given the assumption that the likelihood of survival is only increased if our perceptual apparatus tends to produce true beliefs, it follows that the representational content of our perceptions is by and large correct. In contrast with sceptical hypotheses about perception, non-sceptical explanations require a much smaller number of parameters in their explanation (p. 94). Thus, in comparison, sceptical hypotheses fail to reduce complexity (cf. pp. 90, 94, 98). Consequently, theories which entail that perceptions provide us with truthful access to the world and lead to veritable judgments reduce complexity and are more warranted than their sceptical contenders. However, at this point the question arises whether Peacocke's argument really succeeds in excluding scepticism as a coherent possibility. Even if sceptical hypotheses fail to reduce complexity, I do not see why this excludes the possibility of a Cartesian demon having created a world in which sceptical hypotheses fail to reduce complexity. That is to say, Peacocke's argument only works against a sceptical proposal which accepts that a Cartesian demon could not have created a world in which non-sceptical hypotheses appear complexity reducing. However, it seems hard to see why a sceptic should accept this. Disregarding these challenges, Peacocke even extends his argument: he claims that the correlation between truth and complexity reduction entails in which circumstances a thinker is entitled to make inductive inferences. In particular, Peacocke argues that entitlement to inductive generalisations depends on whether complexity is reduced. That is to say, "when we have a sound, non-conclusive inference from a variety of Fs being G to the conclusion that all Fs are G this holds because the easiest way for the evidence to hold is one that also makes it the case that all Fs are G" (p. 135). Thus far, Peacocke has established that we are entitled to make a transition from one set of mental states to another if the transition is truth-conducive, i.e., if the transition leads to true judgments. He also argues that the truth-conduciveness of a transition can be explained by the nature of the contents and states involved in the transition. This holds for transitions to a priori contents, judgments based on perceptual contents and for some judgments derived from inductive reasoning. In the next step, Peacocke develops his third principle – "The Generalised Rationalist Thesis" – which states that all transitions to which a thinker is entitled are essentially a priori: All instances of the entitlement relation [...] are fundamentally a priori. (p. 148) Peacocke holds that a proposition is a priori if its truth is explicable by the nature and meaning of the contents occurring in the proposition. Correspondingly, a transition is a priori, if its truth-conduciveness is explicable by nature of the contents of the states involved in the transition (p. 152; cf. p. 268). From this conception of the a priori, it is apparent that the third principle is a corollary of his first two principles. To repeat, the first principle holds that a thinker is entitled to make a transition only if it is truth-conducive. The second principle holds that the truth-conduciveness of a transition is to be explained by the nature of the contents and states involved in a transition. Peacocke holds that a transition is a priori if its truthconduciveness can be explained exclusively by the nature and contents of the states involved in a transition. Thus, any transition to which a thinker is entitled is an instance of an a priori transition. Peacocke illustrates how the truth-conducive character of a transition can be derived from the nature of the concepts, contents and states involved in a transition with the example of the concept of the conjunction "p and q" (p. 172). The possessionconditions of a conjunction will consist of the fact that "p and q" is true only if both conjuncts, i.e. p is true and q is true. But if a thinker grasps this possession condition, it entails that she must also accept the transition from "p and q is true" to "p is true", without relying on any (perceptual) experience or conscious state (pp. 172-3). Unfortunately, Peacocke does not provide us with an example clarifying the more controversial claim that the transition between perceptual content and a demonstrative judgment is a priori. Such an example would clearly help to find a better understanding of Peacocke's cardinal thesis that all instances of entitlement are fundamentally a priori. In the last two chapters of the book, Peacocke applies his generalised rationalism to moral thought. He considers this as a test case for examining whether his theory is able to explain the a priori status of moral principles by appeal to the concepts involved therein. Peacocke develops a moral rationalism, which is a middle position between a strong moral realism and subjectivism. He does not hold that our moral beliefs are caused by moral facts, but he also avoids the view that moral claims are subjective and mind dependent. Peacocke claims that the epistemic status of moral principles is similar to that of arithmetic or logic (p. 201). He argues that the key to acquiring moral principles lies in our moral emotions which play a significant role in determining our beliefs about what is right or wrong. According to Peacocke, moral emotions contain representational content which can be assessed as true or false. The truth-value of an emotion is determined by whether an individual experiences an emotion as correct or incorrect. This allows Peacocke to argue that emotions legitimately entitle us to make moral judgements (p. 260). This process of entailment runs analogous to, for instance, our acceptance of a logical proposition by providing a proof for it. In the moral case then, our emotions function as a proof for a moral belief, in the same sense as a "thinker would not have had the belief in the [logical] proposition without perception of a proof" (p. 265). In sum, Peacocke's book represents an impressive defence of a modern rationalism which defines when a thinker is entitled to form a belief irrespective of its content. Peacocke systematically combines theories of rationality, truth and content to an account of entitlement. Indeed, the most valuable aspect of this book is its systematic approach. In particular, Peacocke's skilful employment of the three principles of rationalism and the manner in which he demonstrates how these principles are connected will be enjoyed by anyone interested in a modern defence of rationalism. However, though in his theory Peacocke propagates the special value of complexity reducing explanations, the manner in which he presents parts of his material does not precisely reflect this maxim. Although this will be an obstacle for readers who are new to the field, anyone willing to go deeply into a philosophical discussion will be rewarded by an extremely wide-ranging analysis.