Ralph Wedgwood

This paper offers an account of the a priori. According to this account, the fundamental notion is not that of a priori knowledge, or even of a priori justified belief, but a notion of an a priori justified inferential disposition. The rationality or justification of such a priori justified inferential dispositions is explained purely by some of the basic cognitive capacities that the thinker possesses, independently of any further experiences or other conscious mental states that the thinker happens to have had. It is then shown how a priori justified inferences and beliefs can be explained on the basis of such a priori justified inferential dispositions.

This essay offers an account of the truth conditions of sentences involving deontic modals like ‘ought’, designed to capture the difference between objective and subjective kinds of ‘ought’ This account resembles the classical semantics for deontic logic: according to this account, these truths conditions involve a function from the world of evaluation to a domain of worlds (equivalent to a so-called “modal base”), and an ordering of the worlds in such domains; this ordering of the worlds itself arises from two further elements – a probability function and a value function – since this ordering ranks the worlds in accordance with the expected value of certain propositions that are true at those worlds. Thus, a proposition of the form ‘Ought (p)’ is true at a world of evaluation w if and only if p is true at all the top-ranked worlds in the domain assigned to w. This domain of worlds consists of metaphysically possible worlds, while the probability function is defined over a space of epistemically possible worlds (which may include metaphysically impossible worlds, such as worlds where Hesperus is not Phosphorus). Evidence is given that this account assigns the correct truth conditions to a wide range of sentences involving ‘ought’. Since these truth conditions involve both a domain of metaphysically possible worlds and a space of epistemically possible worlds, there are two corresponding kinds of conditional involving ‘ought’, depending on which space of worlds is restricted by the conditional. Finally, some objections that might be raised against this account are answered.