I am a Tutorial Fellow in Philosophy, at Somerville College in the University of Oxford.

My current research focusses on various issues in ethics. My interests include: foundational issues in consequentialism ('global' and 'two-level' forms of consequentialism), the debate between consequentialists and contractualists, aggregation (utilitarianism, prioritarianism and egalitarianism), moral psychology and selective debunking arguments, population ethics, the interface between ethics and economics, and the analogies between ethics and epistemology.

I also have interests in formal epistemology. My earlier research (until 2011) focussed mainly on philosophy of physics; these interests are now dormant.

Contact information

My papers

Teaching

Email: | hilary dot greaves at philosophy dot ox dot ac dot uk. |

Mailing address: | Somerville College |

Oxford OX2 6HD
UK |

Email is the quickest and most reliable way to reach me.

**Abstract:** Prioritarianism is normally motivated via an appeal to the intuition
that it is better, or more urgent, to benefit the worse off. This paper
argues that that intuition provides no support for the prioritarian thesis.
The argument proceeds via the observation that an equally compelling
intuition of caution --- that in the presence of uncertainty, it is better or
more urgent to improve the worse possible outcomes --- leads, via the
methods that take the prioritarian to prioritarianism, to the precise op-
posite of prioritarianism. The moral of the story is that those methods
are bad ones.

**Abstract:** This article reviews the debate over the value of the social discount
rate, with a particular focus on climate change and on ethical aspects of
the discussion. The review covers the Ramsey equation and its relation-
ship to observed interest rates, the controversy over the rate of pure time
preference, and the discussion of the low discount rate used in the Stern
Review of the Economics of Climate Change.

**Abstract:** Much public policy analysis requires us to place a monetary value on the badness
of a premature human death. Currently dominant approaches to determining
this �value of a life� focus exclusively on the �self-regarding� value of life --- that
is, the value of a person�s life to the person whose death is in question --- and altogether
ignore effects on other people. This procedure would be justified if, as
seems intuitively plausible, other-regarding effects were negligible in comparison
with self-regarding ones. I argue that in the light of the issue of overpopulation,
that intuitively plausible condition is at best highly questionable. Unless the world
is in fact underpopulated, the social disvalue of a premature death is likely to be
significantly lower than the current estimates.

**Abstract:** We provide a rigorous proof of the CPT theorem within the framework
of �Lagrangian� quantum field theory. This is in contrast to the usual rigorous
proofs in purely axiomatic frameworks, and non-rigorous proof-sketches
within the Lagrangian framework.

**Abstract:** I explore the prospects for modelling epistemic rationality (in the
probabilist setting) via an epistemic decision theory, in consequentialist
spirit. Previous work has focussed on cases in which the truth-values
of the propositions in which the agent is selecting credences do not
depend, either causally or merely evidentially, on the agent's choice of
credences. Relaxing that restriction leads to a proliferation of puzzle
cases and theories to deal with them, including epistemic analogues
of evidential and causal decision theory, and of the Newcomb problem
and `Psycho Johnny' problem. A variant of causal epistemic decision
theory deals well with most cases. However, there is a recalcitrant class
of problem cases for which no epistemic decision theory seems able to
match our intuitive judgments of epistemic rationality. This lends
both precision and credence to the view that there is a fundamental
mismatch between epistemic consequentialism and the intuitive notion
of epistemic rationality; the implications for understanding the latter
are briefly discussed.

**Abstract:** It is widely recognised that `global' symmetries, such as the boost
invariance of classical mechanics and special relativity, can give rise to
direct empirical counterparts such as the Galileo-ship phenomenon. How-
ever, conventional wisdom holds that `local' symmetries, such as the dif-
feomorphism invariance of general relativity and the gauge invariance of
classical electromagnetism, have no such direct empirical counterparts.
We argue against this conventional wisdom. We develop a framework
for analysing the relationship between Galileo-ship empirical phenomena
on the one hand, and physical theories that model such phenomena on
the other, that renders the relationship between theoretical and empirical
symmetries transparent, and from which it follows that both global and
local symmetries can give rise to Galileo-ship phenomena. In particular,
we use this framework to exhibit an analog of Galileo's ship for the local
gauge invariance of electromagnetism.

**Abstract:** Structuralism is supposed to be a dissolver of metaphysical pseudo-
debates. This paper is a search for the thesis behind the rhetoric.
Taking `spacetime structuralism' as a case study, I identify six dier-
ent theses that seem to share this name. My conclusions are largely
negative: that those theses that are new are not plausible, and vice
versa. The exception is structuralism as a rejection of the fundamen-
tality of the object/property/relation framework, but in this case it is
as yet unclear what the positive thesis might be.

**Abstract:** The CPT theorem of quantum eld theory states that any rela-
tivistic (Lorentz-invariant) quantum eld theory must also be invari-
ant under CPT, the composition of charge conjugation, parity reversal
and time reversal. This paper sketches a puzzle that seems to arise
when one puts the existence of this sort of theorem alongside a stan-
dard way of thinking about symmetries, according to which spacetime
symmetries (at any rate) are associated with features of the spacetime
structure. The puzzle is, roughly, that the existence of a CPT theo-
rem seems to show that it is not possible for a well-formulated theory
that does not make use of a preferred frame or foliation to make use
of a temporal orientation. Since a manifold with only a Lorentzian
metric can be temporally orientable|capable of admitting a tempo-
ral orientation|this seems to be an odd sort of necessary connection
between distinct existences. The paper then suggests a solution to the
puzzle: it is suggested that the CPT theorem arises because temporal
orientation is unlike other pieces of spacetime structure, in that one
cannot represent it by a tensor field.
To avoid irrelevant technical details, the discussion is carried out
in the setting of classical field theory, using a little-known classical
analog of the CPT theorem.

**Abstract:** Much of the evidence for quantum mechanics is statistical in na-
ture. The Everett interpretation, if it is to be a candidate for serious
consideration, must be capable of doing justice to reasoning on which
statistical evidence in which observed relative frequencies that closely
match calculated probabilities counts as evidence in favour of a the-
ory from which the probabilities are calculated. Since, on the Everett
interpretation, all outcomes with nonzero amplitude are actualized on
di�erent branches, it is not obvious that sense can be made of ascribing
probabilities to outcomes of experiments, and this poses a prima facie
problem for statistical inference. It is incumbent on the Everettian
either to make sense of ascribing probabilities to outcomes of experi-
ments in the Everett interpretation, or to �nd a substitute on which
the usual statistical analysis of experimental results continues to count
as evidence for quantum mechanics, and, since it is the very evidence
for quantum mechanics that is at stake, this must be done in a way
that does not presuppose the correctness of Everettian quantum me-
chanics. This requires an account of theory con�rmation that applies
to branching-universe theories but does not presuppose the correct-
ness of any such theory. In this paper, we supply and defend such an
account. The account has the consequence that statistical evidence
can confirm a branching-universe theory such as Everettian quantum
mechanics in the same way in which it can confirm a probabilistic
theory.

**Abstract:** Richard Feynman has claimed that anti-particles are nothing but
particles `propagating backwards in time'; that time reversing a particle
state always turns it into the corresponding anti-particle state.
According to standard quantum eld theory textbooks this is not so:
time reversal does not turn particles into anti-particles. Feynman's
view is interesting because, in particular, it suggests a nonstandard,
and possibly illuminating, interpretation of the CPT theorem.
This paper explores a classical analog of Feynman's view, in the
context of the recent debate between David Albert and David Malament
over time reversal in classical electromagnetism.

**Abstract:** Recent work in the Everett interpretation has suggested that the problem of probability can be
solved by understanding probability in terms of rationality. However, there are two problems relating
to probability in Everett�one practical, the other epistemic�and the rationality-based program
directly addresses only the practical problem. One might therefore worry that the problem of
probability is only �half solved� by this approach. This paper aims to dispel that worry: a solution to
the epistemic problem follows from the rationality-based solution to the practical problem.

**Abstract:** The Everett (many-worlds) interpretation of quantum mechanics faces a prima facie
problem concerning quantum probabilities. Research in this area has been fast-paced over
the last few years, following a controversial suggestion by David Deutsch that decision
theory can solve the problem. This article provides a non-technical introduction to the
decision-theoretic program, and a sketch of the current state of the debate.

**Abstract:** According to Bayesian epistemology, the epistemically rational agent updates her beliefs
by conditionalisation: that is, her posterior subjective probability after taking
account of evidence X, p_new, is to be set equal to her prior conditional probability
p_old(.|X). Bayesians can be challenged to provide a justification for their claim that
conditionalisation is recommended by rationality - whence the normative force of
the injunction to conditionalise?

There are several existing justifications for conditionalisation, but none directly addresses the idea that conditionalisation will be epistemically rational if and only if it can reasonably be expected to lead to epistemically good outcomes. We apply the approach of cognitive decision theory to provide a justification for conditionalisation using precisely that idea. We assign epistemic utility functions to epistemically rational agents; an agent's epistemic utility is to depend both upon the actual state of the world and on the agent's credence distribution over possible states. We prove that, under independently motivated conditions, conditionalisation is the unique updating rule that maximizes expected epistemic utility.

**Abstract:** Difficulties over probability have often been considered fatal to the
Everett interpretation of quantum mechanics. Here I argue that the Everettian
can have everything she needs from 'probability' without recourse
to indeterminism, ignorance, primitive identity over time or subjective uncertainty:
all she needs is a particular rationality principle.

The decision-theoretic approach recently developed by Deutsch and Wallace claims to provide just such a principle. But, according to Wallace, decision theory is itself applicable only if the correct attitude to a future Everettian measurement outcome is subjective uncertainty. I argue that subjective uncertainty is not available to the Everettian, but I offer an alternative: we can justify Everettian decision theory on the basis that an Everettian should care about all her future branches. The probabilities appearing in the decision-theoretic representation theorem can then be interpreted as the degrees to which the rational agent cares about each future branch. This reinterpretation, however, reduces the intuitive plausibility of one of the Deutsch-Wallace axioms (Measurement Neutrality).