The weakness of must: In defense of a Mantra

Daniel Lassiter


Many semanticists have claimed that must’s meaning is weaker than

epistemic necessity, a claim that von Fintel & Gillies (2010) dub “The Mantra”.

Recently von Fintel & Gillies have argued in an influential paper that the Mantra is

false, and that the intuitions that have driven it can be accounted for by appealing to

evidential meaning. I show that von Fintel & Gillies do not provide a compelling

argument against the Mantra, and that their theory of evidential meaning, while

promising in certain respects, also has serious empirical and conceptual problems.

In addition, a variety of corpus examples indicate that speakers who assert must

p are not always maximally confident in the truth of p. As an alternative, I reimplement

von Fintel & Gillies’ theory of indirect evidentiality in a probabilistic,

Mantra-compatible framework. Ultimately, both sides of the debate are partly right:

must is weak in several respects, but it also encodes an indirect evidential meaning.

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Anand, Pranav & Adrian Brasoveanu. 2010. Modal concord as modal modification. In Proceedings of Sinn und Bedeutung 14, 19–36.

Beaver, David & Brady Clark. 2008. Sense and sensitivity: How focus determines meaning. Wiley-Blackwell.

Danks, David. 2014. Unifying the Mind: Cognitive Representations as Graphical Models. MIT Press.

DeRose, Keith. 1991. Epistemic possibilities. The Philosophical Review 581–605.

von Fintel, Kai & Anthony Gillies. 2008. CIA leaks. The Philosophical Review 117(1). 77.

von Fintel, Kai & Anthony Gillies. 2010. Must... stay... strong! Natural Language Semantics 18(4). 351–383.

Franke, Michael & Tikitu de Jager. 2007. The relevance of awareness. In P. Dekker, M. Aloni & F. Roelofsen (eds.), Proceedings of the Sixteenth Amsterdam Colloquium, 97–102.

Giannakidou, Anastasia. 1999. Affective dependencies. Linguistics and Philosophy 22(4). 367–421.

Giannakidou, Anastasia & Alda Mari. 2014. Epistemic weakening with future and must: Non-veridicality, evidentiality, and partial knowledge. To appear in J. Blaszack (ed.), Tense, Mood, and Modality: New Perspectives on Old Questions. University of Chicago Press.

Ginzburg, Jonathan. 1995. Resolving questions, I. Linguistics and Philosophy 18(5). 459–527.

Glymour, Clark N. 2001. The mind’s arrows: Bayes nets and graphical causal models in psychology. MIT press.

Gopnik, Alison & Laura Schultz (eds.). 2007. Causal Learning: Psychology, Philosophy, and Computation. Oxford University Press.

Groenendijk, Jeroen & Martin Stokhof. 1984. Studies in the Semantics of Questions and the Pragmatics of Answers: University of Amsterdam dissertation.

Grosz, Patrick. 2010. Grading modality: A new approach to modal concord and its relatives. In Proceedings of Sinn und Bedeutung 14, 28–30.

Hacking, Ian. 1967. Possibility. The Philosophical Review 143–168.

Hacquard, Valentine. 2006. Aspects of Modality: Massachusetts Institute of Technology dissertation.

de Jager, Tikitu. 2009. “Now that you mention it, I wonder...”’: Awareness, attention, assumption: University of Amsterdam dissertation.

Karttunen, Lauri. 1972. Possible and must. In J. Kimball (ed.), Syntax and semantics, vol. 1, Seminar Press.

Kemp, C. & J.B. Tenenbaum. 2009. Structured statistical models of inductive reasoning. Psychological Review 116(1). 20-58.

Klecha, Peter. 2012. Positive and conditional semantics for gradable modals. Proceedings of Sinn und Bedeutung 16.

Koller, Daphne & Nir Friedman. 2009. Probabilistic graphical models: Principles and techniques. The MIT Press.

Kratzer, Angelika. 1991. Modality. In von Stechow & Wunderlich (eds.), Semantics: An International Handbook of Contemporary Research, de Gruyter.

Lassiter, Daniel. 2010. Gradable epistemic modals, probability, and scale structure. In N. Li & D. Lutz (eds.), Semantics & Linguistic Theory (SALT) 20, 197–215. CLC Publications.

Lassiter, Daniel. 2011. Measurement and Modality: The Scalar Basis of Modal Semantics: New York University dissertation.

Lassiter, Daniel. 2014a. Epistemic comparison, models of uncertainty, and the disjunction puzzle. Journal of Semantics.

Lassiter, Daniel. 2014b. Measurement and Modality: The Scalar Basis of Modal Semantics. Oxford University Press. To appear.

Lassiter, Daniel. 2014c. Modality, scale structure, and scalar reasoning. Pacific Philosophical Quarterly 95(4): 461-490.

Lassiter, Daniel & Noah D. Goodman. 2013. Context, scale structure, and statistics in the interpretation of positive-form adjectives. In Todd Snider (ed.), Semantics & Linguistic Theory (SALT) 23, 587–610. CLC Publications.

Lassiter, Daniel & Noah D. Goodman. 2014. How many kinds of reasoning? Inference, probability, and natural language semantics. Cognition 136. 123–134.

Lassiter, Daniel & Noah D. Goodman. 2015. Adjectival vagueness in a Bayesian model of interpretation. To appear in Synthese.

MacFarlane, John. 2014. Assessment sensitivity: Relative truth and its applications. Oxford University Press.

Mills, Elizabeth S. 1999. Working with historical evidence: Genealogical principles and standards. National Genealogical Society Quarterly 87(3). 165–84.

Moss, Sarah. 2014. On the semantics and pragmatics of epistemic modals. To appear in Semantics and Pragmatics.

Oaksford, M. & N. Chater. 2007. Bayesian Rationality: The Probabilistic Approach to Human Reasoning. Oxford University Press.

Oaksford, Mike & Nick Chater. 2001. The probabilistic approach to human reasoning. Trends in cognitive sciences 5(8). 349–357.

Osherson, Daniel N., Edward E. Smith, Ormond Wilkie, Alejandro Lopez & Eldar Shafir. 1990. Category-based induction. Psychological review 97(2). 185.

Over, David E. 2009. New paradigm psychology of reasoning. Thinking and Reasoning 15(4).

Palmer, Frank Robert. 1979. Modality and the English modals. Longman London.

Pearl, Judea. 1988. Probabilistic Reasoning in Intelligent Systems: Networks of Plausible Inference. Morgan Kaufmann.

Pearl, Judea. 2000. Causality: Models, reasoning and inference. Cambridge University Press.

Reiter, Raymond. 1980. A logic for default reasoning. Artificial intelligence 13(1). 81–132.

Rips, Lance. 1994. The psychology of proof: Deductive reasoning in human thinking. MIT Press.

Rips, Lance. 2002. Reasoning imperialism. In Renee Elio (ed.), Common Sense, Reasoning, and Rationality, Oxford University Press.

Roberts, Craige. 1996. Information structure in discourse: Towards an integrated formal theory of pragmatics. Working Papers in Linguistics-Ohio State University Department of Linguistics 91–136.

van Rooij, Robert. 2003. Questioning to resolve decision problems. Linguistics and Philosophy 26(6). 727–763.

Russell, Stuart & Peter Norvig. 2010. Artificial Intelligence: A Modern Approach. Prentice Hall.

Sloman, Steven A. 2005. Causal models: How we think about the world and its alternatives. Oxford University Press.

Spirtes, Peter, Clark Glymour & Richard Scheines. 1993. Causation, prediction, and search. MIT press.

Stone, Matthew. 1994. The reference argument of epistemic must. In Proceedings of IWCS 1, 181–190.

Swanson, Eric. 2006. Interactions With Context: MIT dissertation.

Teigen, Karl. 1988. When are low-probability events judged to be ‘probable’? Effects of outcome-set characteristics on verbal probability estimates. Acta Psychologica 68. 157–174.

Tenenbaum, J.B. & T.L. Griffiths. 2001. Generalization, similarity, and bayesian inference. Behavioral and Brain Sciences 24(4). 629–640.

Tenenbaum, J.B., T.L. Griffiths & C. Kemp. 2006. Theory-based bayesian models of inductive learning and reasoning. Trends in cognitive sciences 10(7). 309–318.

Tenenbaum, Joshua B., Charles Kemp, Tom L. Griffiths & Noah D. Goodman. 2011. How to grow a mind: Statistics, structure, and abstraction. Science 331(6022). 1279.

Windschitl, P.D. & G.L. Wells. 1998. The alternative-outcomes effect. Journal of Personality and Social Psychology 75(6). 1411–1423.

Yalcin, Seth. 2005. A puzzle about epistemic modals. MIT Working Papers in Linguistics 51. 231–272.

Yalcin, Seth. 2007. Epistemic modals. Mind 116(464). 983–1026.

Yalcin, Seth. 2010. Probability Operators. Philosophy Compass 5(11). 916–937.

Yalcin, Seth. 2011. Nonfactualism about epistemic modality. In A. Egan & B. Weatherson (eds.), Epistemic Modality, Oxford University Press.