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What are our options? (again)

In decision theory, the available options are often glossed informally as the acts the agent can perform, or the propositions she can make true. But this yields implausible results in cases where an agent has doubts about what she can do.

For example, assume Bob suspects that the button in front of him functions as a light switch, as in fact it does. Then Bob can turn on the light by pressing the button. But if he is not certain that the button is a light switch, decision theory should consider the consequences of pressing the button if it has some other function. So turning on the light by pressing the button should not count as an option.

The Galilean equivalence

It is tempting to think that there is nothing more to physical quantities than their nomic role: that to have a certain mass just is to behave in such-and-such a way under such-and-such conditions.

But it is also tempting to think that the "Galilean equivalence" of inertial mass and gravitational mass is a true identity; i.e., that

Inertial mass = gravitational mass.

However, the role associated with "inertial mass" is completely different from the role associated with "gravitational mass". So if having such-and-such inertial mass is having the relevant dispositions associated with "inertial mass", and likewise for gravitational mass, then the Galilean equivalence could not be an identity. It would rather state an empirical law, according to which two distinct quantities always have the same value.

Effective Altruistism and ethical consumerism

In chapter 8 of Doing Good Better, William MacAskill argues that we should not make a great effort to reduce our carbon emissions, to buy Fairtrade coffee, or to boycott sweatshops. The reason is that these actions have at best a small impact on improving other people's lives and so the cost and effort is better spent elsewhere.

From a strictly utilitarian perspective, there is nothing to complain about this. But strict utilitarianism is a highly counterintuitive position. In fact, MacAskill himself rejects it when he says that it would not be OK to consume meat from factory farms and "offset" by donating to animal welfare organisations, even if the net result would be less animal suffering. I agree. Whether a course of action is right or wrong is not just a matter of the net difference it makes to the amount of suffering in the world. But then we also have to reconsider MacAskill's conclusions about carbon offsetting, fairtrade, and sweatshops.

Mechanistic evidence for probabilistic models

You observe a process that generates two kinds of outcomes, 'heads' and 'tails'. The outcomes appear in seemingly random order, with roughly the same amount of heads as tails. These observations support a probabilistic model of the process, according to which the probability of heads and of tails on each trial is 1/2, independently of the other outcomes.

How observations about frequencies confirm or disconfirm probabilistic models is well understood in Bayesian epistemology. The central assumption that does most of the work is the Principal Principle, which states that if a model assigns (objective) probability x to some outcomes, then conditional on the model, the outcomes have (subjective) probability x. It follows that models that assign higher probability to the observed outcomes receive a greater boost of subjective probability than models that assign lower probability to the outcomes.

IDT again

In my recent post on Interventionist Decision Theory, I suggested that causal interventionists should follow Stern and move from a Jeffrey-type definition of expected utility to a Savage-Lewis-Skyrms type definition. In that case, I also suggested that they could avoid various problems arising from the concept of an intervention by construing the agent's actions as ordinary events. In conversation, Reuben Stern convinced me that things are not so easy.

Brute weak necessities

The two-dimensionalist account of a posteriori (metaphysical) necessity can be motivated by two observations.

First, all good examples of a posteriori necessities follow a priori from non-modal truths. For example, as Kripke pointed out, that his table could not have been made of ice follows a priori from the contingent, non-modal truth that the table is made of wood. Simply taking metaphysical modality as a primitive kind of modality would make a mystery of this fact.

Experts with self-locating beliefs

Imagine you and I are walking down a long path. You are ahead, but we can communicate on the phone. If you say, "there are strawberries here" and I trust you, I should not come to believe that there are strawberries where I am, but that there are strawberries wherever you are. If I also know that you are 2 km ahead, I should come to believe that there are strawberries 2 km down the path. But what's the general rule for deferring to somebody with self-locating beliefs?

Mereological universalism

I used to agree with Lewis that classical mereology, including mereological universalism, is "perfectly understood, unproblematic, and certain". But then I fell into a dogmatic slumber in which it seemed to me that the debate over mereology is somehow non-substantive: that there is no fact of the matter. I was recently awakened from this slumber by a footnote in Ralf Busse's forthcoming article "The Adequacy of Resemblance Nominalism" (you should read the whole thing: it's terrific). So now I once again think that Lewis was right. Let me describe the slumber and the awakening.

Intervenionist decision theory without interventions

Causal models are a useful tool for reasoning about causal relations. Meek and Glymour 1994 suggested that they also provide new resources to formulate causal decision theory. The suggestion has been endorsed by Pearl 2009, Hitchcock 2016, and others. I will discuss three problems with this proposal and suggest that fixing them leads us back to more or less the decision theory of Lewis 1981 and Skyrms 1982.

Sleeping Beauty as losing track of time

What makes the Sleeping Beauty problem non-trivial is Beauty's potential memory loss on Monday night. In my view, this means that Sleeping Beauty should be modeled as a case of potential epistemic fission: if the coin lands tails, any update Beauty makes to her beliefs in the transition from Sunday to Monday will also fix her beliefs on Tuesday, and so the Sunday state effectively has two epistemic successors, one on Monday one on Tuesday. All accounts of epistemic fission that I'm aware of then entail halfing.

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