Bundle theory, originated by the 18th century Scottish philosopher David Hume, is the ontological theory about objecthood in which an object consists only of a collection (bundle) of properties, relations or tropes.
According to bundle theory, an object consists of its properties and nothing more: thus neither can there be an object without properties nor can one even conceive of such an object; for example, bundle theory claims that thinking of an apple compels one also to think of its color, its shape, the fact that it is a kind of fruit, its cells, its taste, or at least one other of its properties. Thus, the theory asserts that the apple is no more than the collection of its properties. In particular, there is no substance in which the properties inhere.
Arguments for the bundle theory
The difficulty in conceiving of or describing an object without also conceiving of or describing its properties is a common justification for bundle theory, especially among current philosophers in the Anglo-American tradition.
The inability to comprehend any aspect of the thing other than its properties implies, this argument maintains, that one cannot conceive of a bare particular (a substance without properties), an implication that directly opposes substance theory. The conceptual difficulty of bare particulars was illustrated by John Locke when he described a substance by itself, apart from its properties, as "something, I know not what."
Whether a relation of an object is one of its properties may complicate such an argument. However, the argument concludes that the conceptual challenge of bare particulars leaves a bundle of properties and nothing more as the only possible conception of an object, thus justifying bundle theory.
Objections to the bundle theory
Objections to bundle theory concern the nature of the bundle of properties, the properties' compresence relation (the togetherness relation between those constituent properties), and the impact of language on understanding reality.
Bundle theory maintains that properties are bundled together in a collection without describing how they are tied together. For example, bundle theory regards an apple as red, four inches (100 mm) wide, and juicy but lacking an underlying substance. The apple is said to be a bundle of properties including redness, being four inches (100 mm) wide, and juiciness.
Critics question how bundle theory accounts for the properties' compresence (the togetherness relation between those properties) without an underlying substance. Critics also question how any two given properties are determined to be properties of the same object if there is no substance in which they both inhere.
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