Online research in philosophy

Many philosophers ponder the question of the a priori status of logical rules like modus ponens. In this paper I argue that the way in which such questions are usually posed is misguided. I argue that to accept modus ponens is nothing else than to have an implication; hence that to ask how do we know that implication obeys modus ponens does not make sense. To ask whether modus ponens is a priori is to ask whether having implication is a priori. I argue that as one is not born with a language (but perhaps only with a predisposition to acquire a certain kind of language, namely one posessing logical vocabulary and hence displaying logical structure), logical rules can be a priori only in the sense that we tend to acquire language governed by such rules.

The terms "a priori" and "a posteriori" refer primarily to how or on what basis a proposition might be known. A proposition is knowable a priori if it is knowable independently of experience. A proposition is knowable a posteriori if it is knowable on the basis of experience. The a priori/a posteriori distinction is epistemological and should not be confused with the metaphysical distinction between the necessary and the contingent or the semantical or logical distinction between the analytic and the synthetic. Two aspects of the a priori/a posteriori distinction require clarification: the conception of experience on which the distinction turns; and the sense in which a priori knowledge is independent of such experience. The latter gives rise to important questions regarding the positive basis of a priori knowledge.

Introduction: Three key principles -- Sense datum theories -- Adverbial theories -- Belief acquisition theories -- Intentional theories -- Disjunctive theories -- Perception and causation -- Perception and the sciences of the mind -- Perception and other sense modalities.

Significant attention has been paid to Berkeley's account of perception; however, the interpretations of Berkeley's account of perception by suggestion are either incomplete or mistaken. In this paper I begin by examining a common interpretation of suggestion, the 'Propositional Account'. I argue that the Propositional Account is inadequate and defend an alternative, non-propositional, account. I then address George Pitcher's objection that Berkeley's view of sense perception forces him to adopt a 'non-conciliatory' attitude towards common sense. I argue that Pitcher's charge is no longer plausible once we recognize that Berkeley endorses the non-propositional sense of mediate perception. I close by urging that the non-propositional interpretation of Berkeley's account of mediate perception affords a greater appreciation of Berkeley's attempt to bring a philosophical account of sense perception in line with some key principles of common sense. While Berkeley's account of perception and physical objects permits physical objects to be immediately perceived by some of the senses, they are, most often, mediately perceived. But for Berkeley this is not a challenge to common sense since common sense requires only that we perceive objects by our senses and that they are, more or less, as we perceive them. Mediate perception by suggestion is, for Berkeley, as genuine a form of perception as immediate perception, and both are compatible with Berkeley's understanding of the demands of common sense.

Recent defenses of a priori knowledge can be applied to the idea of conventions in science in order to indicate one important sense in which conventionalism is correctsome elements of physical theory have a unique epistemological status as a functionally a priori part of our physical theory. I will argue that the former a priori should be treated as empirical in a very abstract sense, but still conventional. Though actually coming closer to the Quinean position than recent defenses of a priori knowledge, the picture of science developed here is very different from that developed in Quinean holism in that categories of knowledge can be differentiated.

In what follows, I argue that Hume works with a notion of the a priori that, though unfamiliar today, was standard in the seventeenth and eighteenth centuries. On this notion of the a priori, to know (consider, prove) something a priori is to know (consider, prove) it from the grounds that make it true. I will refer to this as the "from-grounds" notion of the a priori, and to the now-familiar and dominant notion—on which to know something a priori is to know it with a justification that is independent of experience—as the "non-empirical" notion.Hume holds, as a substantive thesis, that one knows something a priori, where 'a priori' is understood in the from-grounds sense, only if one knows it independently of ..