Introduction

In Extended Rationality. A Hinge Epistemology, I put forward a moderate account of perceptual justification, according to which a belief about specific material objects that P is perceptually justified iff, absent defeaters, one has the appropriate course of experience (typically an experience with content that P), and it is assumed that H “there is an external world” (and possibly other general propositions, like “My sense organs work mostly reliably,” “I am not the victim of massive cognitive deception,” etc.).

Since, in my view, “There is an external world” is a “hinge” proposition—for it makes the acquisition of perceptual justification possible—, the crucial issue is to determine the nature of hinge assumptions. Do they have to be doxastically assumed by a subject in the process of offering a justification for her belief that P, or can we think of these assumptions as being operative at the propositional level? And what would that mean?

In this chapter, I defend various interlocking claims. First, that there is a legitimate sense in which hinge assumptions are to be cashed out, first and foremost, at the propositional level, or “in the abstract space of reasons.” Second, that this does not preempt the possibility that they also obtain at the doxastic level (§1). To such an end, I spell out what assuming a hinge proposition at the doxastic level amounts to, in such a way that even subjects who do not have the conceptual resources to entertain its content may be granted with such an assumption.

I then distinguish three possible senses of assuming doxastically that H (§2): one hypothetical, one categorial, and one factual. I claim that while both the second and the third sense are compatible with the moderate account of perceptual justification, only the second is compatible with the development of a nondogmatic response to skepticism and is therefore preferable.

Along the way, I compare and contrast my account of hinge assumptions with Gilbert Harman's and, in closing I defend it from objections raised by Crispin Wright (§3).