the Extensional Device

An Extensional Device is a conceptual tool used in logic and mathematics to distinguish objects based on their external characteristics or identities. Essentially, it looks at the way objects are uniquely identified by their properties or their relationships with other objects. For example, in set theory, two sets are considered equal if they contain exactly the same elements. The Extensional Device emphasizes this external, observable aspect, allowing us to determine object identity and equality through their external features rather than internal or intrinsic qualities.