Ifs and Oughts

Journal of Philosophy 107 (3):115-143 (2010)
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We consider a paradox involving indicative conditionals (‘ifs’) and deontic modals (‘oughts’). After considering and rejecting several standard options for resolv- ing the paradox—including rejecting various premises, positing an ambiguity or hidden contextual sensitivity, and positing a non-obvious logical form—we offer a semantics for deontic modals and indicative conditionals that resolves the paradox by making modus ponens invalid. We argue that this is a result to be welcomed on independent grounds, and we show that rejecting the general validity of modus ponens is compatible with vindicating most ordinary uses of modus ponens in reasoning.



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Author Profiles

John MacFarlane
University of California, Berkeley
Niko Kolodny
University of California, Berkeley

Citations of this work

The Normativity of Rationality.Benjamin Kiesewetter - 2017 - Oxford: Oxford University Press.
Ought, Agents, and Actions.Mark Schroeder - 2011 - Philosophical Review 120 (1):1-41.
Opting for the Best: Oughts and Options.Douglas W. Portmore - 2019 - New York, NY, USA: Oxford University Press.
The Importance of Being Rational.Errol Lord - 2013 - Dissertation, Princeton University

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References found in this work

A counterexample to modus ponens.Vann McGee - 1985 - Journal of Philosophy 82 (9):462-471.
Meaning and speech acts.R. M. Hare - 1970 - Philosophical Review 79 (1):3-24.
Duty and Ignorance of Fact.H. A. Prichard - 1932 - Philosophy 8 (30):226-228.
On a Supposed Counterexample to Modus Ponens.Bernard D. Katz - 1999 - Journal of Philosophy 96 (8):404.

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