Tom Reid meets Tom Bayes: A defense of common sense

Thomas Reid is often misread as defending common sense, if at all, only by relying on illicit premises about God or our natural faculties. On these theological or reliabilist misreadings, Reid makes common sense assertions where he cannot give arguments. This paper attempts to untangle Reid’s defense of common sense by distinguishing four arguments: (a) the argument from madness, (b) the argument from natural faculties, (c) the argument from impotence, and (d) the argument from practical commitment. Of these, (a) and (c) do rely on problematic premises that are no more secure than claims of common sense itself. Yet (b) and (d) do not. This conclusion can be established directly by considering the arguments informally, but one might still worry that there is an implicit premise in them. In order to address this concern, I reconstruct the arguments in the framework of subjective Bayesianism. The worry becomes this: Do the arguments rely on specific values for the prior probability of some premises? Reid’s appeals to our prior cognitive and practical commitments do not. Rather than relying on specific probability assignments, they draw on things that are part of the Bayesian framework itself, such as the nature of observation and the connection between belief and action. Contra the theological or reliabilist readings, the defense of common sense does not require indefensible premises. ∗Earlier versions of this material appeared in [Mag03] and [Mag04], and an earlier draft of this paper was presented at the ’Hume and his Critics’ conference in April, 2005. I would like to thank Stephen Boulter, Gordon Graham, Ryan Nichols, Susan Purviance, and Ken Westphal for helpful comments and questions at the conference; I would also like to thank Todd Buras and Margaret Tate at Baylor University for organizing the conference. Thanks also to anonymous referees.