In this paper I argue that de Finetti provided compelling reasons for rejecting countable additivity. It is ironical therefore that the main argument advanced by Bayesians against following his recommendation is based on the consistency criterion, coherence, he himself developed. I will show that this argument is mistaken. Nevertheless, there remain some counter-intuitive consequences of rejecting countable additivity, and one in particular has all the appearances of a full-blown paradox. I will end by arguing that in fact it is no (...) paradox, and that what it shows is that conditionalisation, often claimed to be integral to the Bayesian canon, has to be rejected as a general rule in a finitely additive environment. (shrink)

In this article, I first elaborate and refine the Principle of Intention Agglomeration (PIA), which was introduced by Michael Bratman as “a natural constraint on intention”. According to the PIA, the intentions of a rational agent should be agglomerative. The proposed refinement of the PIA is not only in accordance with the spirit of Bratman’s planning theory of intention as well as consistency constraints for intentions rooted in the theory, but also reveals some deep rationales of practical rationality regarding resource-limited (...) agents. Then I defend the PIA against various objections and counterexamples, showing that the refined PIA survives attacks based on both conceptual analyses and psychological considerations. (shrink)

Here are two plausible ideas about belief. First: beliefs are our means of storing information. Second: if we believe something, then we are willing to use it in reasoning. But in this paper I introduce a puzzle that seems to show that these cannot both be right. The solution, I argue, is a new picture, on which there is a kind of belief for each idea. An account of these two kinds of belief is offered in terms of two components: (...) a relatively stable one, which represents our information; and a more variable one, which represents what we are taking seriously. I also consider the possibility of solving the puzzle by less radical means; and an alternative argument for the proposed account of belief in terms of considerations from desire. (shrink)

This essay answers the “Bayesian Challenge,” which is an argument offered by Bayesians that concludes that belief is not relevant to rational action. Patrick Maher and Mark Kaplan argued that this is so because there is no satisfactory way of making sense of how it would matter. The two ways considered so far, acting as if a belief is true and acting as if a belief has a probability over a threshold, do not work. Contrary to Maher and Kaplan, Keith (...) Frankish argued that there is a way to make sense of how belief matters by introducing a dual process theory of mind in which decisions are made at the conscious level using premising policies . I argue that Bayesian decision theory alone shows that it is sometimes rational to base decisions on beliefs; we do not need a dual process theory of mind to solve the Bayesian Challenge. This point is made clearer when we consider decision levels : acting as if a belief is true is sometimes rational at higher decision levels. (shrink)

Leibniz seems to have been the first to suggest a logical interpretation of probability, but there have always seemed formidable mathematical and interpretational barriers to implementing the idea. De Finetti revived it only, it seemed, to reject it in favour of a purely decision-theoretic approach. In this paper I argue that not only is it possible to view (Bayesian) probability as a continuum-valued logic, but that it has a very close formal kinship with classical propositional logic.

There are many ordinary propositions we think we know. Almost every ordinary proposition entails some "lottery proposition" which we think we do not know but to which we assign a high probability of being true (for instance: “I will never be a multi-millionaire” entails “I will not win this lottery”). How is this possible - given that some closure principle is true? This problem, also known as “the Lottery puzzle”, has recently provoked a lot of discussion. In this paper I (...) discuss one of the most promising answers to the problem: Stewart Cohen’s contextualist solution which is based on ideas about the salience of chances of error. After presenting some objections to it I sketch an alternative solution which is still contextualist in spirit. (shrink)