Exploring A New Argument for Synchronic Chance

A synchronic probability is the probability at a time that an outcome occurs at that very time. Common sense invokes synchronic probabilities with values between 0 and 1 (e.g., the probability right now that the top card of this deck is presently the ace of spades is 1/52), as do scientific theories such as classical statistical mechanics. Recently, philosophers have argued about whether any synchronic probabilities are best interpreted as objective chances. I add to this debate an underappreciated reason we might have to believe in synchronic chance; it might turn out that the best interpretation of our common sense and scientific theories is one in which the macrophysical properties of physical systems are partly determined by synchronic chance distributions over microphysical properties of those systems. Additionally, I argue against the common charge that synchronic probability fails to satisfy various platitudes about chance—most notably Lewis’s (1986) Principal Principle. 0. Introduction In normal conversational contexts, we casually refer to the probability that the top card of this fair deck is presently the ace of spades (which is about 2%), to the probability that most of the lemons on my tree are now ripe (which is high this time of year), and to the probability that an arbitrarily selected student from my introductory philosophy class is currently scoring a Bor better (which is about 50%). In other words, we speak as if there are non-extremal probabilities (i.e., probabilities with values between 0 and 1) at a time that an event occurs at that very time. And this phenomenon isn’t limited to common-sense discourse: classical statistical mechanics, for example, assigns nonextremal probabilities at a time to various ways the particles of a gas might be arranged at that very time.