Hannes Matthiessen

Defeasibility, most generally speaking, means that given some set of conditions A, something else B will hold, unless or until defeating conditions C apply. While the term was introduced into philosophy by legal philosopher H.L.A. Hart in 1949, today, the concept of defeasibility is employed in many different areas of philosophy. This volume for the first time brings together contributions on defeasibility from epistemology , legal philosophy and ethics and the philosophy of action . The volume ends with an extensive bibliography.

George Berkeley argues that vision is a language of God, that the immediate objects of vision are arbitrary signs for tactile objects and that there is no necessary connection between what we see and what we touch. Thomas Reid, on the other hand, aims to establish a geometrical connection between visible and tactile figures. Consequently, although Reid and Berkeley's theories of vision share important elements, Reid explicitly rejects Berkeley's idea that visible figures are merely arbitrary signs for tangible bodies. But is he right in doing so? I show that many passages in Berkeley's work on vision suggest that he acknowledges a geometrical connection between visibles and tangibles. So the opposition between the arbitrariness Berkeley defends and a geometrical connection cannot be as universal as Reid thinks. This paper seeks to offer a plausible reading of Berkeley's theory of vision in this regard and an explanation of why Reid interprets Berkeley differently.

Thomas Reid's Geometry of Visibles, according to which the geometrical properties of an object's perspectival appearance equal the geometrical properties of its projection on the inside of a sphere with the eye in its centre allows for two different interpretations. It may (1) be understood as a theory about phenomenal visual space – i.e. an account of how things appear to human observers from a certain point of view – or it may (2) be seen as a mathematical model of viewpoint-relative but mind-independent relational properties of objects. This paper makes a systematic and a historical claim. I shall argue, first, that given certain features of the human visual system phenomenal visual space differs in several aspects from Reidean visual space. Secondly, I suggest that, since Reid was aware of some of these empirical facts, we should interpret Reid as endorsing the second interpretation of the Geometry of Visibles.

In Epistemic Entitlement. The Right to Believe Hannes Ole Matthiessen develops a social externalist account of epistemic entitlement and perceptual knowledge. The basic idea is that positive epistemic status should be understood as a specific kind of epistemic right, that is a right to believe. Since rights have consequences for how others are required to treat the bearer of the right, they have to be publicly accessible. The author therefore suggests that epistemic entitlement can plausibly be conceptualized as a status that is grounded in a publicly observable perceptual situation, rather than in a perceptual experience as current theories of epistemic entitlement state. It is then argued that such a social externalist account of entitlement, in which the perceiver's epistemic perspective becomes relevant only in the exceptional case where an entitlement is challenged, can nevertheless do justice to our central intuitions about first-personal epistemic phenomenology.

According to Paul Snowdon, one directly perceives an object x iff one is in a position to make a true demonstrative judgement of the form “That is x”. Whenever one perceives an object x indirectly (or dependently , as Snowdon puts it) it is the case that there exists an item y (which is not identical to x) such that one can count as demonstrating x only if one acknowledges that y bears a certain relation to x. In this paper I argue that what we hear directly are sounds, and that material objects (such as violins and goldfinches) are only indirectly heard. However, there are cases of auditory object perception that should count as direct : Some blind persons’ ears are so sensitive to the way sound waves are modified by things in their surroundings that they can detect objects such as other persons, fences or trees. Interestingly, objects localized in this way make themselves felt via a kind of pressure in the perceiver’s face (that is why the phenomenon is commonly called “facial vision”), the perception is phenomenally quite different from hearing. Since, to some degree, most people are able to conclude from the way it sounds that, say, they stand at the foot of a concrete wall (when there is enough traffic noise around), we can imagine situations where two persons perceive the same wall, one indirectly (demonstratively apprehending sounds) and the other directly (demonstratively apprehending nothing but the wall). These cases invite us to discuss the role phenomenology plays in determining whether an object is perceived directly or indirectly.

In recent epistemological literature, epistemic entitlement is understood as a personal epistemic status that does not require elaborate justificatory activity on behalf of the entitled individual. It is nevertheless internalist in a weaker sense, since it is said to be grounded in perceptual experiences. It seems, however, that the conditions under which an epistemic right holds should, like in cases of most other rights, be publicly observable, because they have implications for the ways others are required to treat the entitled individual. Therefore I suggest an alternative to the weakly internalist conception of epistemic entitlement as based on mental episodes. I show how we can construe epistemic rights as being based on external conditions that are publicly observable. This social externalist approach is then defended against internalist and externalist challenges.

Thomas Reid argued that the geometrical properties of visible figures equal the geometrical properties of their projections on the inside of a sphere centred around the eye. In recent scholarship there are only a few suggestions of which sources might have inspired Reid. I point to a widely ignored body of early eighteenth-century literature – introductions into projective geometry, the use of celestial globes and astronomy – in which the model of the eye in the centre of a sphere was immensely popular. Moreover, I argue that Reid's account results naturally from some astronomical doctrines in conjunction with George Berkeley's theory of vision.