Editing Universal (metaphysics) (section)

==Problem of universals==
{{Main|Problem of universals}}
The [[problem of universals]] is an ancient problem in metaphysics on the existence of universals. The problem arises from attempts to account for the phenomenon of [[Similarity (philosophy)|similarity]] or attribute agreement among things.<ref>Loux (1998), p. 20; (2001), p. 3.</ref> For example, [[grass]] and [[Granny Smith|Granny Smith apples]] are similar or agree in attribute, namely in having the attribute of greenness. The issue is how to account for this sort of agreement in attribute among things.

There are many philosophical positions regarding universals. Taking "[[beauty]]" as an example, four positions are:
* [[Idealism]]: beauty is a property constructed in the mind, so it exists only in descriptions of things.
* [[Platonic realism|Platonic extreme realism]]: beauty is a property that exists in an ideal form independently of any mind or thing.
* [[Aristotle's theory of universals|Aristotelian moderate realism]] or [[conceptualism]]: beauty is a property of things (''fundamentum in re'')<ref>Cfr. Georg Jánoska, "Das ''Fundamentum in re'' im Nominalismus", in: ''Kant-Studien'' Volume 55: Issue 1-4 DOI: https://doi.org/10.1515/kant.1964.55.1-4.439 | Published online: 04 Sep 2009</ref> that the mind abstracts from these beautiful things.
* [[Nominalism]]: there are no universals, only individuals.

Taking a broader view, the main positions are generally considered classifiable as: [[Philosophical realism|extreme realism]], [[nominalism]] (sometimes simply named "anti-realism" with regard to universals),<ref>MacLeod & Rubenstein (2006), §3.</ref> [[moderate realism]], and [[idealism]]. Extreme Realists posit the existence of independent, abstract universals to account for attribute agreement. Nominalists deny that universals exist, claiming that they are not necessary to explain attribute agreement. Conceptualists posit that universals exist only in the [[philosophy of mind|mind]], or when conceptualized, denying the independent existence of universals, but accepting they have a ''fundamentum in re''. 
Complications which arise include the implications of language use and the complexity of relating language to [[ontology]].