Editing Abstract and concrete (section)

==In philosophy<!--'Third Realm (Frege)' redirects here-->==
The [[type–token distinction]] identifies physical objects that are tokens of a particular type of thing.<ref>Carr, Philip (2012) "The Philosophy of Phonology" in ''Philosophy of Linguistics'' (ed. Kemp, Fernando, Asher), Elsevier, p. 404</ref>  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 [[paradigm|paradigmatic]] examples of objects of each kind:

{| class="wikitable"
|-
|+ Examples of abstract and concrete objects
|-
!'''Abstract'''
!'''Concrete'''
|-
| Tennis
| A tennis match
|-
| Redness
| Red light reflected off of an apple and hitting one's eyes
|-
| Five
| Five cars
|-
| Justice
| A just action
|-
| Humanity (the property of being human)
| Human population (the set of all humans)
|-
|}

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 [[Metaphysical naturalism|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.

Some, such as [[Ernst Mally]],<ref>[https://mally.stanford.edu/mally.html Ernst Mally – The Metaphysics Research Lab]</ref> [[Edward Zalta]]<ref name=SEP/> and arguably, [[Plato]] in his [[Theory of Forms]],<ref name=SEP/> have held that abstract objects constitute the defining subject matter of [[metaphysics]] or philosophical inquiry more broadly. To the extent that philosophy is independent of empirical research, and to the extent that empirical questions do not inform questions about abstracta, philosophy would seem especially suited to answering these latter questions.

In [[modern philosophy]], the distinction between abstract and concrete was explored by [[Immanuel Kant]]<ref>''[[Critique of Pure Reason|KrV]]'' A51/B75–6. See also: Edward Willatt, ''Kant, Deleuze and Architectonics'', Continuum, 2010 p. 17: "Kant argues that cognition can only come about as a result of the union of the abstract work of the understanding and the concrete input of sensation."</ref> and [[G. W. F. Hegel]].<ref>Georg Wilhelm Friedrich Hegel: ''[[The Science of Logic]]'', Cambridge University Press, 2010, p. 609. See also: Richard Dien Winfield, ''Hegel's Science of Logic: A Critical Rethinking in Thirty Lectures'', Rowman & Littlefield Publishers, 2012, p. 265.</ref>

[[Gottlob Frege]] said that abstract objects, such as propositions, were members of a third realm,<ref>[[Gottlob Frege]], "Der Gedanke. Eine logische Untersuchung", in: ''Beiträge zur Philosophie des deutschen Idealismus'' 1 (1918/19), pp. 58–77; esp. p. 69.</ref> different from the external world or from internal [[consciousness]].<ref name="Rosen" /> (See [[Popper's three worlds]].)

===Abstract objects and causality===
Another popular proposal for drawing the abstract–concrete distinction contends that an object is abstract if it lacks [[causality|causal]] power. A causal power has the ability to affect something causally. Thus, the empty set is abstract because it cannot act on other objects. One problem with this view is that it is not clear exactly what it is to have causal power. For a more detailed exploration of the abstract–concrete distinction, see the relevant ''[[Stanford Encyclopedia of Philosophy]]'' article.<ref name=SEP>{{cite SEP |url-id=abstract-objects |title=Abstract Objects |last=Rosen |first=Gideon}}</ref>

===Quasi-abstract entities<!--'Quasi-abstract' redirects here-->===
In the 2010s, there was some philosophical interest in the development of a third category of objects known as the '''quasi-abstract'''<!--boldface per WP:R#PLA-->. Quasi-abstract objects have drawn particular attention in the area of [[social ontology]] and [[documentality]]. Some argue that the over-adherence to the [[Platonism|platonist]] duality of the concrete and the abstract has led to a large category of social objects having been overlooked or rejected as [[Nonexistent object|nonexistent]] because they exhibit characteristics that the traditional duality between concrete and abstract regards as incompatible.<ref>B. Smith (2008), "Searle and De Soto: The New Ontology of the Social World". In ''The Mystery of Capital and the Construction of Social Reality''. Open Court.</ref> Specifically, the ability to have temporal location, but not spatial location, and have causal agency (if only by acting through representatives).<ref>{{cite journal |first1=E. H. |last1=Robinson |url=http://www.edwardheath.net/wp-content/uploads/2013/01/Social_Agentivity.pdf |title=A Theory of Social Agentivity and Its Integration into the Descriptive Ontology for Linguistic and Cognitive Engineering |journal=[[International Journal on Semantic Web and Information Systems]] |volume=7 |issue=4 |date=2011 |pages=62–86 |doi=10.4018/ijswis.2011100103 |url-status=dead |archive-url=https://web.archive.org/web/20170810075924/http://www.edwardheath.net/wp-content/uploads/2013/01/Social_Agentivity.pdf |archive-date= Aug 10, 2017 }}</ref> These characteristics are exhibited by a number of social objects, including states of the international legal system.<ref>E. H. Robinson (2014), "A Documentary Theory of States and Their Existence as Quasi-Abstract Entities", ''Geopolitics'' '''19''' (3), pp. 1–29.</ref>