bundle theory a view that accepts the idea that concrete objects consist of properties but denies the need for introducing substrata to account for their diversity. By contrast, one traditional view of concrete particular objects is that they are complexes consisting of two more fundamental kinds of entities: properties that can be exemplified by many different objects and a substratum that exemplifies those properties belonging to a particular object. Properties account for the qualitative identity of such objects while substrata account for their numerical diversity.
The bundle theory is usually glossed as the view that a concrete object is nothing but a bundle of properties. This gloss, however, is inadequate. For if a ‘bundle’ of properties is, e.g., a set of properties, then bundles of properties differ in significant ways from concrete objects. For sets of properties are necessary and eternal while concrete objects are contingent and perishing.
A more adequate statement of the theory holds that a concrete object is a complex of properties which all stand in a fundamental contingent relation, call it co-instantiation, to one another. On this account, complexes of properties are neither necessary nor eternal. Critics of the theory, however, maintain that such complexes have all their properties essentially and cannot change properties, whereas concrete objects have some of their properties accidentally and undergo change. This objection fails to recognize that there are two distinct problems addressed by the bundle theory: (a) individuation and (b) identity through time. The first problem arises for all objects, both momentary and enduring. The second, however, arises only for enduring objects. The bundle theory typically offers two different solutions to these problems. An enduring concrete object is analyzed as a series of momentary objects which stand in some contingent relation R. Different versions of the theory offer differing accounts of the relation. For example, Hume holds that the self is a series of co-instantiated impressions and ideas, whose members are related to one another by causation and resemblance (this is his bundle theory of the self). A momentary object, however, is analyzed as a complex of properties all of which stand in the relation of co-instantiation to one another. Consequently, even if one grants that a momentary complex of properties has all of its members essentially, it does not follow that an enduring object, which contains the complex as a temporal part, has those properties essentially unless one endorses the controversial thesis that an enduring object has its temporal parts essentially. Similarly, even if one grants that a momentary complex of properties cannot change in its properties, it does not follow that an enduring object, which consists of such complexes, cannot change its properties. Critics of the bundle theory argue that its analysis of momentary objects is also problematic. For it appears possible that two different momentary objects have all properties in common, yet there cannot be two different complexes with all properties in common. There are two responses available to a proponent of the theory. The first is to distinguish between a strong and a weak version of the theory. On the strong version, the thesis that a momentary object is a complex of co-instantiated properties is a necessary truth, while on the weak version it is a contingent truth. The possibility of two momentary objects with all properties in common impugns only the strong version of the theory. The second is to challenge the basis of the claim that it is possible for two momentary objects to have all their properties in common. Although critics allege that such a state of affairs is conceivable, proponents argue that investigation into the nature of conceivability does not underwrite this claim. See also ESSENTIALISM , IDENTITY OF INDIS- CERNIBLES , METAPHYSICS , PHENOMENALISM , SUBSTANCE , TIME SLIC. A.C.