Non-physical entity

In ontology and the philosophy of mind, a non-physical entity is an object that exists outside physical reality. The philosophical schools of idealism and dualism assert that such entities exist, while physicalism asserts that they do not. Positing the existence of non-physical entities leads to further questions concerning their inherent nature and their relation to physical entities. Abstract and concrete Abstraction Philosophers generally do agree on the existence of abstract objects. The mind can conceive of objects that clearly have no physical counterpart. Such objects include concepts such as numbers, mathematical sets and functions, and philosophical relations and properties. If such objects are indeed entities, they are entities that exist only in the mind itself, not within space and time. For an example, an abstract property such as redness has no presence in space-time. To make a distinction between metaphysics and epistemology, such objects, if they are to be considered entities, are categorized as logical entities to distinguish them from physical entities. The study of non-physical entities can be summarized by the question, "Is imagination real?" While older Cartesian dualists held the existence of non-physical minds, more limited forms of dualism propounded by 20th and 21st century philosophers (such as property dualism) hold merely the existence of non-physical properties. Mind–body dualism Dualism is the division of two contrasted or opposed aspects. The dualist school supposes the existence of non-physical entities, the most widely discussed one being the mind. But beyond that it runs into stumbling blocks. Pierre Gassendi put one such problem directly to René Descartes in 1641, in response to Descartes's Meditations: [It] still remains to be explained how that union and apparent intermingling [of mind and body ...] can be found in you, if you are incorporeal, unextended and indivisible [...].