The Aristotelian Society

The Aristotelian Society

est. 1880

2016 Joint Session

Symposium III

John MacFarlane | Joint Session of the Aristotelian Society and the Mind Association | University of Warwick

vagueness as indecision

John MacFarlane (Berkeley)


This paper motivates and explores an expressivist theory of vagueness, modeled on Allan Gibbard’s (2003) normative expressivism. It shows how Chris Kennedy’s (2007) semantics for gradable adjectives can be adjusted to fit into a theory on Gibbardian lines, where assertions constrain not just possible worlds but plans for action. Vagueness, on this account, is literally indecision about where to draw lines. It is argued that the distinctive phenomena of vagueness, such as the intuition of tolerance, can be explained in terms of practical constraints on plans, and that the expressivist view captures what is right about several contending theories of vagueness.



John MacFarlane is Professor of Philosophy at the University of California, Berkeley. He has worked on a wide variety of topics in the history of philosophy, epistemology, the philosophy of logic and mathematics, and the philosophy of language. He is the author of Assessment Sensitivity: Relative Truth and Its Applications (OUP, 2014).

Robert Williams | Joint Session of the Aristotelian Society and the Mind Association | University of Warwick

vagueness as indecision

robert williams (leeds)


Paint being red is one thing; it is another for a person to treat paint as red for some practical purpose. The first is a matter of the paint and its properties; the second involves activity: placing the pot on a particular shelf, fetching it in response to verbal instructions,etc. 

This essay explores the thesis that for vague predicates uncertainty over whether a borderline instance x of red/large/tall/good is to be understood as practical uncertainty over whether to treat x as red/large/tall/good. Expressivist/quasi-realist treatments of vague predicates due to John MacFarlane and Daniel Elstein provide the stalking horse. Section 1 introduces a question about our attitudes to borderline cases of vague predicates F. Section 2 explores the actions of treating and/or counting a thing as F. Section 3 reviews how we might share our practical plans to count-as-F and evaluate those plans. Section 4 looks at the shapes that the best plans to count-as-F may take. Section 5 links these practical evaluations to the cognitive evaluations of doxastic attitudes to vague predications. Sections 6 and 7 concern puzzles for the approach suggested here. Section 6 explores its treatment of normatively defective or contested terms, and section 7 raises a puzzle about the mechanics of MacFarlane’s detailed implementation of the approach in connection to gradable adjectives.


Robert Williams is Professor of Theoretical Philosophy at the University of Leeds. He joined Leeds in 2005, after graduate work in Oxford and St Andrews. His areas of research include logic and rationality, conditionals and conditional thinking, and the metaphysics of mind and language. He is currently engaged in writing two monographs, one on the nature of representation and another on indeterminacy, the former supported by an ERC research grant.

further info


Cardiff University

8 - 10 July 2016

School of English, Communication and Philosophy
John Percival Building
Cardiff University
Colum Road
Cardiff CF10 3EU

Local Organisers: Nicholas Shackel

Programme edited by Matthew Soteriou (Warwick)

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