Abstract

While the concept of multiple realizability is widely used, it is seldom rigorously characterized. This paper defends a liberal conception of multiple realizability as sameness of type through _any_ differences in the (lower-level) conditions that give rise to instances of that type. This kind of “sameness through difference” is contrasted with another type of asymmetric dependency relation between properties, multiple _specification_. This liberal conception is then defended from objections, and it is augmented by a concept of relativized multiple realizability. The last section presents a survey of the ontological, explanatory, and methodological consequences of this analysis of multiple realizability.