Abstract

Any abstractionist approach to thin objects faces the threat of paradox, as illustrated by Frege’s inconsistent Basic Law V. The neo-Fregeans Hale and Wright respond by severely restricting the class of acceptable abstraction principles. Their approach is _static_ in the sense that they hold the domain fixed. This approach to abstraction is criticized, and an alternative approach is developed which permits abstraction on a vast class of equivalence relations. This alternative approach is _dynamic_ in the sense that abstraction on an extensionally specified domain (i.e. a domain specified by means of a plurality of objects) may result in a larger such domain. A form of absolute generality is nevertheless possible, provided that the associated domain is understood in an intensional sense (i.e. it cannot be specified by means of a plurality).