Michael Shaffer

In a recent article, Peter Gärdenfors (1992) has suggested that the AGM (Alchourrón, Gärdenfors, and Makinson) theory of belief revision can be given an epistemic basis by interpreting the revision postulates of that theory in terms of a version of the coherence theory of justification. To accomplish this goal Gärdenfors suggests that the AGM revision postulates concerning the conservative nature of belief revision can be interpreted in terms of a concept of epistemic entrenchment and that there are good empirical reasons to adopt this view as opposed to some form of foundationalist account of the justification of our beliefs. In this paper I argue that Gärdenfors’ attempt to underwrite the AGM theory of belief revision by appealing to a form of coherentism is seriously inadequate for several reasons.

Following Nancy Cartwright and others, I suggest that most theories incorporate, or depend on, one or more idealizing assumptions. I then argue that such theories ought to be regimented as counterfactuals, the antecedents of which are simplifying assumptions. If this account of the logical form of theories is granted, then a serious problem arises for Bayesians concerning the prior probabilities of theories that have counterfactual form. If no such probabilities can be assigned, then posterior probabilities will be undefined, as the latter are defined in terms of the former. I argue here that the most plausible attempts to address the problem of probabilities of conditionals fail to help Bayesians, and, hence, that Bayesians are faced with a new problem. In so far as these proposed solutions fail, I argue that Bayesians must give up Bayesianism or accept the counterintuitive view that no theories that incorporate any idealizations have ever really been confirmed to any extent whatsoever. Moreover, as it appears that the latter horn of this dilemma is highly implausible, we are left with the conclusion that Bayesianism should be rejected, at least as it stands.

This book is addresses a topic that has received little or no attention in orthodox epistemology. Typical epistemological investigation focuses almost exclusively on knowledge, where knowing that something is the case importantly implies that what is believed is strictly true. This condition on knowledge is known as factivity and it is, to be sure, a bit of epistemological orthodoxy. So, if a belief is to qualify as knowledge according to the orthodox view it cannot be false. There is also an increasingly influential group of epistemologists who argue that one ought to act only on what one knows, because truth of belief is the surest way to guarantee that our actions work out as planned. They defend what is known as the knowledge norm for action. This view is typically justified in virtue of the idea that successful intentional action should stem from knowledge because knowledge is a factive propositional attitude and it is, as a result, success-prone with respect to intentional action. In other words, true beliefs that constitute knowledge are the rationally normative standard for successful acting. But, there are clearly multitudes of cases where epistemic agents operate successfully and even rationally on the basis of beliefs that are false. That this is the case is not especially controversial. Sometimes false beliefs facilitate successful action. Of course, this can be because the agent is simply lucky. However, there is something particularly important about some false beliefs that relates to successful action but not in virtue of luck. While not strictly true, the beliefs in question are close to the truth or approximately true. This gives rise to the possibility that there are knowledge-like states that play roles very similar to knowledge but which are only quasi-factive. That is to say such states imply approximate truth and do not imply strict truth. Moreover, often such beliefs facilitate successful action in virtue of their being approximately true and this suggests a much more plausible norm for successful action that encompasses both cases of rational action guided by such quasi-factive states as well as cases of rational action guided by knowledge. The thesis of this book is that quasi-factive knowledge-like states are far more common that epistemologists have acknowledge and the book introduces a theory of such states and how they give rise to a much more reasonable account of the norms for action. This involves some tricky issues concerning approximate truth, the rationality of believing not strictly true claims, the justification of approximately true beliefs, the nature of false but approximately true evidence, the norms of belief, knowledge and quasi-knowledge, etc.

It has been argued that the presence of idealizations in physical theories implies that scientific realism is false. Furthermore, it has also been argued that because physical theories incorporate idealizations scientific theories must be accepted a priori, because the objects, processes, etc. quantified over in such expressions cannot be observed in the actual world. I argue against the former view by showing that scientific realism is compatible with the fact that all theoretical claims depend on idealizing assumptions, at least when such claims are properly regimented as a special kind of counterfactual conditional. To this end a logic incorporating such conditionals, VCP, is constructed and given a semantic basis. Given VCP, the latter problem is considered in light of extant theories of confirmation, and all are found to be incapable of dealing with the acceptance of theoretical claims that depend on idealizing assumptions. In addressing this problem it is also shown that a new problem arises for subjective Bayesians concerning prior probabilities of theoretical claims that depend on idealizing assumptions. Insofar as I claim that all theoretical claims depend on idealizing assumptions, this problem for Bayesian confirmation theory appears to be quite serious. I conclude that only inference to the best explanation, when understood in terms of VCP, can provide a rational basis for the empirical acceptance of such theoretical claims