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Lewis's argument for Humility

In "Ramseyan Humility", Lewis argues for a thesis he calls "Humility". He never quite says what that thesis is, but its core seems to be the claim that our evidence can never rule out worlds that differ from actuality merely by swapping around fundamental properties. Lewis's argument, on pp.205-207, is perhaps the most puzzling argument he ever gave.

Lewis begins with some terminology.

A note on the scaling of desirability

In The Logic of Decision, Richard Jeffrey pointed out that the desirability (or "news value") of a proposition can be usefully understood as a weighted average of the desirability of different ways in which the proposition can be true, weighted by their respective probability. That is, if A and B are incompatible propositions, then

(1) Des(AvB) = Des(A)P(A/AvB) + Des(B)P(B/AvB).

So desirabilities are affected by probabilities. If you prefer A over B and just found out that conditional on their disjunction, A is more likely then B, then the desirability of the disjunction goes up. That seems right.

Owned possibility and unowned ability

Superficially, modal auxiliaries such as 'must', 'may', 'might', or 'can' seem to be predicate operators. So it is tempting to interpret them as functions from properties to properties: just as 'Alice jumps' attributes to Alice the property of jumping, 'Alice can jump' attributes to her the property of being able to jump, 'Alice may jump' attributes the property of being allowed to jump, and so on.

Perhaps the biggest obstacle to this approach comes from quantified constructions. If 'Alice may jump' attributes to Alice the property of being allowed to jump, then 'one of us may jump' should say that one of us has the property of being allowed to jump. But while this is one possible reading of the sentence, 'one of us may jump' also has a reading on which it states that it is permissible that one of us jumps. There is a kind of de re/de dicto ambiguity here, which suggests that 'may' can not only apply to properties but also to propositions.

Does subjective uncertainty objectively matter?

Let's say that an act A is subjectively better than an alternative B if A is better in light of the agent's information; A is objectively better if it is better in light of all the facts. The distinction is easiest to grasp in a consequentialist setting. Here an act is objectively better if it brings about more good -- if it saves more lives, for example. A morally conscientious agent may not know which of her options would bring about more good. Her subjective ranking of the options might therefore go by the expectation of the good: by the probability-weighted average of the good each act might bring about.

Abstracts on the Philosopher's Index

"The Philosopher's Index" is a commercial software once widely used to search for articles in philosophy journals. These days it is generally easier and faster to search on the open internet. (Even the company behind the Philosopher's Index is not quite sure why the Index is still needed.) However, there is one thing the Index has that can't be found anywhere else: many of its entries contain abstracts of books and articles, apparently provided by the authors themselves. These abstracts are often not part of the published versions, and they can be quite useful to get an authoritative summary, or to see what the author considered to be the main point of a paper.

Microequiprobability

If you spin a wheel of fortune, the outcome -- red or black -- depends on the speed with which you spin. As you increase the speed, the outcome quickly cycles through the two possibilities red and black. As a consequence, any reasonably smooth probability distribution (or frequency distribution) over initial speed determines an approximately equal probability (frequency) for red and black. Here is an example of such a distribution, taken from Strevens.

An allegedly microequiprobable distribution

Notes on Strevens, Bigger than Chaos

I've been asked to review Michael Strevens's new book, Tychomancy. This motivated me to have another look at his earlier book Bigger than Chaos.

The aim of Bigger than Chaos is to explain how apparently chaotic interactions in highly complex systems often give rise to simple large-scale regularities, such as the laws of thermodynamics, the stability of predator/prey population levels, or the economic cycle. The basic explanatory strategy, which Strevens calls enion probability analysis (EPA), consists in aggregating the probabilistic dynamics for the individual components of a complex system into a probabilistic dynamics for macro-level features of the system.

Centred propositions and agent-relative value

Plausible moral theories should be agent-relative. They should permit us to care more about close friends than about distant strangers. They can prohibit killing ten innocent people even in circumstances where eleven innocent people would otherwise be killed by somebody else. They might say that it would be right for Alice to dance with Bob, but wrong for Bob to dance with Alice.

But how should we think about agent-relative values? It may seem that the state of affairs in which Alice dances with Bob is either right or not right. How could it be right relative to Alice but wrong relative to Bob? Or consider a case where I can prevent you from killing eleven by killing ten myself. If it is wrong that you kill the eleven, then surely I have a moral reason to see to it that you don't kill the eleven, just as I have a moral reason to see to it that I don't kill the ten. Moreover, presumably it is worse if you kill eleven than if I kill ten. So shouldn't my reason to prevent you from killing the eleven outweigh my reason to not kill the ten?

Indeterminacy of representation and representation of indeterminacy

Often the factors that determine a phenomenon don't determine it uniquely. Sometimes this changes the phenomenon itself.

Take language. Plausibly, the meanings of our words are somehow determined by patterns of use, but these patterns aren't specific enough to fix, say, a unique extension or intension for our language. There is a range of precise meaning assignments all of which fit our use equally well. One might leave it at that and say that it is indeterminate which of these precise languages we speak. But this misses something. It misses the fact that we don't speak a precise language. For example, in a precise language, "Mount Everest has sharp boundaries" would be true, but in English it is false. The logic of a precise language would (arguably) be classical, but the logic of English is not.

Back to ratificationism?

When we face a decision and work out what we should do, we gain information about what we will do. Taking into account this information can in turn affect what we should do. Here's an example.

(I) In front of you are two opaque boxes, one black one white. You can open one of them and keep whatever is inside. Yesterday, a perfect (or almost perfect) predictor tried to predict what you would choose. If she predicted that you'd take the black box, she put a million dollars in the white box and two dollars in the black box. If she predicted that you'd take the white box, she put a thousand dollars in the black box and one dollar in the white box. Which box do you open?

Let's say that at the beginning of your deliberation, you are completely undecided, giving 50 percent credence to the hypothesis that you'll end up opening the black box. Standard formulations of causal decision theory then say that opening the white box has greater expected payoff: since there's a 50 percent probability that it contains a million, the expected payoff is 500000.50, which is a lot more than what you could possibly find in the black box. However, choosing to open the white box would provide you with highly relevant information: it would reveal that the predictor has (almost certainly) put only one dollar in the white box and a thousand in the black box. As a rational decision-maker you should take that information into account. Many putative "counterexamples" to causal decision theory, such as those in Richter 1985 and Egan 2007, are based on this observation.

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