Lorne Falkenstein

Reid's Inquiry into the Human Mind on the Principles of Common Sense devotes more space to double vision than to any other topic. In what follows, I examine why this subject was so important to Reid and why he dealt with it as he did. I also consider whether his argument for his position begs the question against his main opponents, Berkeley and Robert Smith. I show that, as Reid presented it, it does, but that he could have said more than he did in reply to Smith. My discussion of why double vision was important for Reid begins with an exposition of the relevance of the theory of vision for one of Reid's principal concerns in the Inquiry: the concern to respond to scepticism concerning our knowledge of an external world. I then turn to consider how Reid's account of double vision contributes to his epistemological realism and why the alternative account offered by Berkeley and Smith challenges it.

: I argue that Condillac was committed to four mutually inconsistent propositions: that the mind is unextended, that sensations are modifications of the mind, that colours are sensations, and that colours are extended. I argue that this inconsistency was not just the blunder of a second-rate philosopher, but the consequence of a deep-seated tension in the views of early modern philosophers on the nature of the mind, sensation, and secondary qualities and that more widely studied figures, notably Condillac's contemporaries, Hume and Reid, were not ultimately any more successful at developing an account of vision that unproblematically avoids the paradox. In passing, I take issue with Nicholas Pastore's account of how Condillac's Treatise on Sensations deals with the visual perception of form (in A Selective History of Theories of Visual Perception)

Hume had two principal arguments for denying that we can have an idea of a vacuum, an argument from the non-entity of unqualified points and an argument from the impossibility of forming abstract ideas of manners of disposition. He also made two serious concessions to the opposed view that we can indeed form ideas of vacua, namely, that bodies that have nothing sensible disposed between them may permit the interposition of other bodies without any apparent motion or occlusion and that it is possible to conceive the contents of a room to be evacuated without being compelled to conceive the walls moving into contact. To reconcile these concessions with his arguments and show why we only “falsely imagine” that we can form the idea of a vacuum, Hume developed a psychological theory of the perception of “invisible and intangible distance” that has something in common with Berkeley’s account of the perception of outward distance. This paper argues that this theory is both untenable and inconsistent with fundamental Humean principles. It explains why Hume should have rejected the two arguments against the idea of a vacuum and why accepting ideas of vacua would have been more in line with the rest of his thought than attempting to deny that we have any such ideas.