The
type–token distinction identifies physical objects that are tokens of a particular type of thing. The "type" of which it is a part is in itself an abstract object. The abstract–concrete distinction is often introduced and initially understood in terms of
paradigmatic examples of objects of each kind: Abstract objects have often garnered the interest of philosophers because they raise problems for popular theories. In
ontology, abstract objects are considered problematic for
physicalism and some forms of
naturalism. Historically, the most important ontological dispute about abstract objects has been the
problem of universals. In
epistemology, abstract objects are considered problematic for
empiricism. If abstracta lack causal powers and spatial location, how do we know about them? It is hard to say how they can affect our sensory experiences, and yet we seem to agree on a wide range of claims about them. In
philosophy of religion, the existence of abstract objects is sometimes considered a problem for
divine aseity, which, for example, prompted the Christian philosopher
William Lane Craig to argue against uncreated abstract objects. Other Christian philosophers, such as
Peter van Inwagen, have conversely argued
for their existence, seeing no conflict between them and
theism. Some, such as
Ernst Mally,
Edward Zalta and
G. W. F. Hegel.
Gottlob Frege said that abstract objects, such as propositions, were members of a third realm, different from the external world or from internal
consciousness.
Quasi-abstract entities In the 2010s, there was some philosophical interest in the development of a third category of objects known as the
quasi-abstract. Quasi-abstract objects have drawn particular attention in the area of
social ontology and
documentality. Some argue that an over-adherence to the
platonist duality of the concrete and the abstract has led to a large category of social objects having been overlooked or rejected as
nonexistent because they exhibit characteristics that the traditional duality between concrete and abstract regards as incompatible. Specifically, the ability to have temporal location, but not spatial location, and have causal agency (if only by acting through representatives). These characteristics are exhibited by a number of social objects, including states of the international legal system. ==In psychology==