Button: Internal categoricity and internal realism in the philosophy of mathematics

UNIVERSITY SEMINAR ON LOGIC, PROBABILITY, AND GAMES
Internal categoricity and internal realism in the philosophy of mathematics

Tim Button (University of Cambridge)
4:10 pm, Wednesday, April 19th, 2017
Faculty House, Columbia University

Abstract. Many philosophers think that mathematics is about ‘structure’. Many philosophers would also explicate this notion of ‘structure’ via model theory. But the Compactness and Löwenheim–Skolem theorems lead to some famously hard questions for this view. They threaten to leave us unable to talk about any particular ‘structure’.

In this talk, I outline how we might explicate ‘structure’ without appealing to model theory, and indeed without invoking any kind of semantic ascent. The approach involves making use of internal categoricity. I will outline the idea of internal categoricity, state some results, and use these results to make sense of Putnam’s beautiful but cryptic claim: “Models are not lost noumenal waifs looking for someone to name them; they are constructions within our theory itself, and they have names from birth.”

Koellner: Gödel’s Disjunction

UNIVERSITY SEMINAR ON LOGIC, PROBABILITY, AND GAMES
Gödel’s Disjunction
Peter Koellner (Harvard University)
5:00 pm, Friday, April 7th, 2017
716 Philosophy Hall, Columbia University

Abstract. Gödel’s disjunction asserts that either “the mind cannot be mechanized” or “there are absolutely undecidable statements.” Arguments are examined for and against each disjunct in the context of precise frameworks governing the notions of absolute provability and truth. The focus is on Penrose’s new argument, which interestingly involves type-free truth. In order to reconstruct Penrose’s argument, a system, DKT, is devised for absolute provability and type-free truth. It turns out that in this setting there are actually two versions of the disjunction and its disjuncts. The first, fully general versions end up being (provably) indeterminate. The second, restricted versions end up being (provably) determinate, and so, in this case there is at least an initial prospect of success. However, in this case it will be seen that although the disjunction itself is provable, neither disjunct is provable nor refutable in the framework.

Parikh: An Epistemic Generalization of Rationalizability

UNIVERSITY SEMINAR ON LOGIC, PROBABILITY, AND GAMES
An Epistemic Generalization of Rationalizability
Rohit Parikh (CUNY)
4:10 pm, Friday, March 24th, 2017
Faculty House, Columbia University

Abstract. Rationalizability, originally proposed by Bernheim and Pearce, generalizes the notion of Nash equilibrium. Nash equilibrium requires common knowledge of strategies. Rationalizability only requires common knowledge of rationality. However, their original notion assumes that the payoffs are common knowledge. I.e. agents do know what world they are in, but may be ignorant of what other agents are playing.

We generalize the original notion of rationalizability to consider situations where agents do not know what world they are in, or where some know but others do not know. Agents who know something about the world can take advantage of their superior knowledge. It may also happen that both Ann and Bob know about the world but Ann does not know that Bob knows. How might they act?

We will show how a notion of rationalizability in the context of partial knowledge, represented by a Kripke structure, can be developed.

Gaifman and Liu: A Simpler and More Realistic Subjective Decision Theory

UNIVERSITY SEMINAR ON LOGIC, PROBABILITY, AND GAMES
Essential Simplifications of Savage’s Subjective Probabilities System
Haim Gaifman (Columbia University) and
Yang Liu (University of Cambridge)
4:10 pm, Friday, November 18th, 2016
Faculty House, Columbia University

Abstract. This talk covers: (I)  A short outline of Savage’s system; (II) A new mathematical technique for handling “partitions with errors” that leads to a simplification that Savage tried but did not succeed in getting, which leads to the definition of numerically precise probabilities without the σ-algebra assumption; (III) Some philosophical analysis of the notion of idealized rational agent, which is commonly used as a guideline for subjective probabilities.

Some acquaintance with Savage’s system is helpful, but (I) is added in order to make for a self-contained presentation. The talk is based on a joint work by the authors titled “A Simpler and More Realistic Subjective Decision Theory”. Please email Robby for an introductory section of the present draft of the paper.

More about the seminar here.

We will be having dinner right after the meeting at the faculty house. Please let Robby know if you will be joining us so that he can make an appropriate reservation (please be advised that at this point the university only agrees to cover the expenses of the speaker and the rapporteur and that the cost for all others is $30, payable by cash or check).

Price: Heart of DARCness

UNIVERSITY SEMINAR ON LOGIC, PROBABILITY, AND GAMES
Heart of DARCness
Huw Price (University of Cambridge)
4:10 pm, Thursday, October 13th, 2016
Faculty House, Columbia University

Abstract. Alan Hajek has recently criticised the thesis that Deliberation Crowds Out Prediction (renaming it the DARC thesis, for ‘Deliberation Annihilates Reflective Credence’). Hajek’s paper has reinforced my sense that proponents and opponents of this thesis often talk past one other. To avoid confusions of this kind we need to dissect our way to the heart of DARCness, and to distinguish it from various claims for which it is liable to be mistaken. In this talk, based on joint work with Yang Liu, I do some of this anatomical work. Properly understood, I argue, the heart is in good shape, and untouched by Hajek’s jabs at surrounding tissue. Moreover, a feature that Hajek takes to be problem for the DARC thesis – that it commits us to widespread ‘credal gaps’ – turns out to be a common and benign feature of a broad class of cases, of which deliberation is easily seen to be one.

More about the seminar here.

We will be having dinner right after the meeting at the faculty house. Please let Robby know if you will be joining us so that he can make an appropriate reservation (please be advised that at this point the university only agrees to cover the expenses of the speaker and the rapporteur and that the cost for all others is $30, payable by cash or check).

Workshop on Group Agency and Social Epistemology

groupagencyworkshop

Date: April 2nd, 10:00.  Location: Phil 716.


Philip Kitcher
Social Agnotology

Agnotology stands to ignorance as epistemology stands to knowledge. This talk will be focused on social mechanisms that sustain ignorance. Some forms of ignorance are fruitful. Most are not. I begin with some distinctions. Those distinctions are then used to consider particularly noxious (and live) forms of contemporary ignorance: specifically, kinds of ignorance that persist in spite of knowledgeable people within the community, and that endure because those who remain ignorant cannot tell who is expert with respect to an important debated issue (example – confusions about anthropocentric climate change). I argue that the intellectual credit economy, useful in sustaining valuable diversity within the scientific community, interacts with other valuable social conditions (wide recognition that scientists should inform the general public) to erode the markers of epistemic authority on which all of us depend.

Cailin O’Connor
Power, Bargaining, and Evolution

Nash famously showed that power differences across players in game theoretic models can translate into advantages in bargaining scenarios. In this talk, I discuss joint work with Justin Bruner where we explore how power, hashed out in several different ways, can lead to bargaining advantage in evolving social populations. I show how these models can inform the emergence of norms of collaboration across hierarchies in academia, and other bargaining norms in populations with more and less powerful groups.

Gregory Wheeler
Mispriced gambles: What peers learn when they disagree

The Preservation of Irrelevant Evidence (PIE) Principle maintains that a resolution strategy to peer disagreements should be able to preserve unanimous judgments of evidential irrelevance among the peers. It is well-known that no standard Bayesian resolution strategy satisfies the PIE Principle, and some — such as Carl Wagner — have argued so much the worse for PIE. In this paper we respond by giving a loss aversion argument in support of PIE and against Bayes. Another response is for each peer to dig in her heels and remain ‘steadfast’ or cave-in to a single dictator. Thomas Kelly advocates the former approach and nobody, so far as I know, the latter. In any case, we respond by arguing that a disagreement introduces to the peers the serious possibility that they may have mispriced the random quantities in dispute. The theory of imprecise probability offers tools to clear up these matters, but it also uncovers new issues that are unfamiliar to standard probabilistic modelings for a single agent. Thus, we introduce the notion of a set-based credal judgment to frame and address some of that subtleties that arise in peer disagreements.

Kevin Zollman
The credit economy and the economic rationality of science

Scientists are motivated by the credit they are given for their discoveries by their peers. Traditional theories of the scientific method in philosophy do not include this motivation, and at first blush it appears as though these theories would regard it as inappropriate. A number of scholars have suggested, however, that this motivation serves to perpetuate successful science. It has been proposed as a mechanism to encourage more scientific effort and a mechanism to effectively allocate resources between competing research programs. This paper presents an economic model of scientists’ choices in which these claims can be formalized and evaluated. Ultimately, the paper comes to mixed conclusions. The motivation for credit may help to increase scientists effort in science, but also may serve to misallocate effort between competing research programs.