*Accuracy and the Laws of Credence* (Oxford University Press) is out now!

On this page, I’ll be posting details of reviews of the book, together with supplementary material that might be useful for people reading it — I hope to include video tutorials on some of the technical aspects of the book, for instance.

# Overview

In this book, we offer an extended investigation into a particular way of justifying the rational principles that govern our credences (or degrees of belief). The main principles that we justify are the central tenets of Bayesian epistemology, though we meet many other related principles along the way. These are: Probabilism, the claims that credences should obey the laws of probability; the Principal Principle, which says how credences in hypotheses about the objective chances should relate to credences in other propositions; the Principle of Indifference, which says that, in the absence of evidence, we should distribute our credences equally over all possibilities we entertain; and Conditionalization, the Bayesian account of how we should plan to respond when we receive new evidence. Ultimately, then, the book is a study in the foundations of Bayesianism.

To justify these principles, we look to decision theory. We treat an agent’s credences as if they were a choice she makes between different options. We give an account of the purely epistemic utility enjoyed by different sets of credences. And we appeal to the principles of decision theory to show that, when epistemic utility is measured in this way, the credences that violate the principles listed above are ruled out as irrational. The account of epistemic utility we give is the veritist’s: the sole fundamental source of epistemic utility for credences is their accuracy. Thus, this is an investigation in the version of epistemic utility theory known as accuracy-first epistemology. The book can also be read as an extended reply on behalf of the veritist to the evidentialist’s objection that veritism cannot account for certain evidential principles of credal rationality, such as the Principal Principle, the Principle of Indifference, and Conditionalization.

# Sample material

Here is the introduction to the book (PDF).

# Reviews and Symposia

## Book symposium in *Philosophy and Phenomenological Research*

- Précis (PDF)
- Jim Joyce (Michigan Ann Arbor) (website)
- R. A. Briggs (Stanford) (website)
- Matt Kotzen (UNC Chapel Hill) (website)
- Responses (PDF)

## Book symposium in *Episteme*

*Episteme *14(1):1-69

- Précis and replies (PDF)
- Contribution from Fabrizio Cariani (PDF)
- Contribution from Sophie Horowitz (PDF)
- Contribution from Ben Levinstein (PDF)
- Contribution from Julia Staffel (PDF)

## Reviews

- Notre Dame Philosophical Reviews (Kenny Easwaran)
- Philosophy of Science (Chad Marxen and Gerard Rothfus)
- Metascience (Erik Olsson)
- Journal of Philosophy (R. A. Briggs)
- Mind (Scott Sturgeon)

# Supplementary material

## Talks

- This talk, which I gave at the Trends in Logic conference at University of Ghent in 2014, gives an overview of the topics covered in the book.

## Video tutorials

In these video tutorials, I run through some of the more technical material from the book. (The tutorials are made with the ShowMe app.)

- Definition of a probability function (Defn 1.0.1) (stream)
- Definition of a convex hull (Defn I.A.1) (stream)
- Conditional probability, the ratio formula, and the Theorem of Total Probability (stream)
- De Finetti’s Characterization Theorem (Thm I.A.2) (stream)
- Connection between Bregman divergences and strictly proper scoring rules (stream)
- Mathematics of the Dutch Book argument 1 – formulating the theorem (stream) (handout)
- Mathematics of the Dutch Book argument 2 – proving the theorem (stream) (handout)
- Dominance Theorem for Bregman Divergences – (Lemma I.D.6 (Case A)) (stream)

## Jonathan Weisberg’s *Accuracy for Dummies* blogs

- Part 1: Euclid Improper
- Part 2: from Euclid to Brier
- Part 3: Beyond the Second Dimension
- Part 4: Euclid in the Round
- Part 5: Convexity
- Part 6: Obtusity
- Part 7: Dominance

# Errata

- page 5: on the second line of the equation at the top of the page, the second summand should include the subscript ‘w1’ rather than ‘w2’
- page 146: second bullet point.
**ETP+**should say that*c*is in the closure of the convex hull of*C*_*E*(*C*subscript*E*).