Red Herrings: Some Thoughts on the Meaning of Zero-Probability Events and Mathematical Modeling By Edi Karni* Abstract: Kicking off the discussion following Savage's presentation at the 1952 Paris colloquium, Arrow raised what he considered to be a difficulty with the intuitive interpretation of Savage's theorem. It suggests that decision makers strictly prefer betting on an event of measure zero over betting on a proper subset of that event. Within the realm of the revealed-preference methodology and limited verifiability, Arrow's difficulty is a red herring: the problem he poses has it origin in technical aspects of the Savage's model and not in the substantive aspect of it. Keywords: Zero-probability events, Null events, revealed preference JEL Classification: D8 * Department of Economics, Johns Hopkins University. E-mail address karni@jhu.edu . I benefited from discussions and comments with Itzhak Gilboa, Joseph Greenberg, Dov Samet, Marco Scarsini, and David Schmeidler. None of them is responsible for or necessarily shares the views expressed in this note.