Rachael Briggs

Decision-Theoretic Paradoxes as Voting Paradoxes

It is a platitude among decision theorists that agents should choose their actions so as to maximize expected value. But exactly how to define expected value is contentious. Evidential decision theory (henceforth EDT), causal decision theory (henceforth CDT), and a theory proposed by Ralph Wedgwood that I will call benchmark theory (BT) all advise agents to maximize different types of expected value. Consequently, their verdicts sometimes conflict. In certain famous cases of conflict-medical Newcomb problems-CDT and BT seem to get things right, while EDT seems to get things wrong. In other cases of conflict, including some recent examples suggested by Egan 2007, EDT and BT seem to get things right, while CDT seems to get things wrong. In still other cases, EDT and CDT seem to get things right, while BT gets things wrong.

Truthmaking without necessitation

I propose an account truthmaking that provides truthmakers for negative truths. The account replaces Truthmaker Necessitarianism with a “Duplication Principle”, according to which a suitable entity T is a truthmaker for a proposition p just in case the existence of an appropriate counterpart of T entails the truth of p, where the counterpart relation is cashed out in terms of qualitative duplication. My account captures an intuitive notion of truthmakers as “things the way they are”, validates two appealing principles about entailment and containment proposed by David Armstrong, and invalidates the controversial Disjunction Thesis.

The big bad bug bites anti-realists about chance

David Lewis’s ‘Humean Supervenience’ (henceforth ‘HS’) combines realism about laws, chances, and dispositions with a sparse ontology according to which everything supervenes on the overall spatiotemporal distribution of non-dispositional properties (Lewis 1986a, Philosophical papers: Volume II, pp. ix–xvii, New York: Oxford Univesity Press, 1994, Mind 103:473–490). HS faces a serious problem—a “big bad bug” (Lewis 1986a, p. xiv): it contradicts the Principal Principle, a seemingly obvious norm of rational credence. Two authors have tried to rescue Lewis’s ontology from the ‘big bad bug’ (henceforth ‘the Bug’) by rejecting realism about laws, chances, and dispositions (Halpin 1994, Aust J Phil 72:317–338, 1998, Phil Sci 65:349–360; Ward 2005, Phil Sci 71:241–261). I will argue that this strategy cannot possibly work: it is the ontology, not the realist thesis, that lies at the root of the problem.

Costs of abandoning the Sure-Thing Principle

Risk-weighted expected utility theory (REU theory for short) permits preferences which violate the Sure-Thing Principle (STP for short). But preferences that violate the STP can lead to bad decisions in sequential choice problems. In particular, they can lead decision-makers to adopt a strategy that is dominated – i.e. a strategy such that some available alternative leads to a better outcome in every possible state of the world.

Unavoidable decoherence in the quantum control of an unknown state

Abstract A common objective for quantum control is to force a quantum system, initially in an unknown state, into a particular target subspace. We show that if the subspace is required to be a decoherence-free subspace of dimension greater than 1, then such control must be decoherent. That is, it will take almost any pure state to a mixed state. We make no assumptions about the control mechanism, but our result implies that for this purpose coherent control offers no advantage, in principle, over the obvious measurement-based feedback protocol.

Foundations of Probability

The foundations of probability are viewed through the lens of the subjectivist interpretation. This article surveys conditional probability, arguments for probabilism, probability dynamics, and the evidential and subjective interpretations of probability.

Epistemic dispositions. Reply to Turri and Bronner

We reply to recent papers by John Turri and Ben Bronner, who criticise the dispositionalised Nozickian tracking account we discuss in “Mad, Bad and Dangerous to Know.” We argue that the account we suggested can handle the problems raised by Turri and Bronner. In the course of responding to Turri and Bronner’s objections, we draw three general lessons for theories of epistemic dispositions: that epistemic dispositions are to some extent extrinsic, that epistemic dispositions can have manifestation conditions concerning circumstances where their bearers fail to exist, and that contrast is relevant to disposition attributions.