On Knowing What is Necessary: Three Limitations of Peacocke's Account

Chapter 4 of Being Known outlines an integrated metaphysics and epistemology for the metaphysical-absolute-notions of necessity and possibility. The leading idea is to view the modal status of a proposition as the deliverance of a set of fundamental Principles of Possibility, and our ability to recognise modal status as issuing from an implicit knowledge of these principles. Peacocke aims at a middle way between the extremes of Lewisstyle realism about modality and the various-conventionalist, expressivist, Wittgensteinian-forms of non-cognitivism that were prominent in the last century. An attraction of his account is its unified treatment both of a priori logical-more generally, conceptual-necessity and possibility and of a posteriori necessities of essence, identity, origin and constitution, etc. The treatment is ambitious and rich in invention and original detail, but Peacocke professes himself (p. 191)1 more wedded to the general approach than to the particular development. I shall correspondingly confine my remarks, more or less, to the general approach. Here is the briefest sketch of it. The Principles of Possibility govern the notion of an admissible assignment of semantic values to the ingredient concepts in a (set of) proposition(s). Foremost among them, the Modal Extension Principle (MEP) determines that an assignment is admissible only if each concept is allotted a semantic value which results from applying the same rule as determines its actual semantic value. An assignment to bachelor, for instance, respects the MEP only if it provides that concept with an extension determined as the intersection of those it provides for unmarried and man, while an assignment to a de jure rigid concept, like Christopher Peacocke, respects the constraint only if it provides that concept with its actual semantic value. Next come a battery of Constitutive Principles