Editing Problem of universals (section)

==Ancient philosophy==
The problem of universals is considered a central issue in traditional metaphysics and can be traced back to [[Plato]] and [[Aristotle]]'s philosophy,<ref>{{Cite book|last=Stamos|first=David N.|title=The Species Problem: Biological Species, Ontology, and the Metaphysics of Biology|url=https://archive.org/details/speciesproblembi00stam_262|url-access=limited|publisher=Lexington Books|year=2003|isbn=0-7391-0503-5|location=Lanham, MD|pages=[https://archive.org/details/speciesproblembi00stam_262/page/n9 8]}}</ref> particularly in their attempt to explain the nature and status of forms.<ref>{{Cite book|last=Loux|first=Michael J.|title=Metaphysics: Contemporary Readings|publisher=Routledge|year=2001|isbn=0-415-26108-2|location=London|pages=3}}</ref> These philosophers explored the problem through [[Predication (philosophy)|predication]].

=== Plato ===
Plato believed that there was a sharp distinction between the world of perceivable objects and the world of universals or [[substantial form|forms]] (eidos): one can only have mere opinions about the former, but one can have [[knowledge]] about the latter. For Plato, it was not possible to have knowledge of anything that could change or was particular, since knowledge had to be forever unfailing and general.<ref>MacLeod & Rubenstein (2006), §1b.</ref> For that reason, the world of the forms is the real world, like [[Allegory of the cave|sunlight]], while the sensible world is only imperfectly or partially real, like [[Allegory of the cave|shadows]]. This [[Platonic realism]], however, in denying that the [[theory of forms|eternal Forms]] are mental artifacts, differs sharply with modern forms of idealism.

One of the first nominalist critiques of Plato's realism was that of [[Diogenes of Sinope]], who said "I've seen Plato's cups and table, but not his cupness and tableness."<ref>{{cite book|last=Davenport|first=Guy|others=Translated by Guy Davenport|title=Herakleitos and Diogenes|publisher=Grey Fox Press|location=Bolinas|year=1979|pages=[https://archive.org/details/herakleitosdioge00hera/page/57 57]|isbn=0-912516-35-6|url=https://archive.org/details/herakleitosdioge00hera/page/57}}</ref>

=== Aristotle ===
{{See also|Aristotelian realist philosophy of mathematics}}
Plato's student Aristotle disagreed with his tutor. Aristotle transformed Plato's forms into "[[Four causes#Formal cause|formal causes]]", the blueprints or [[essence]]s of individual things. Whereas Plato idealized [[geometry]], Aristotle emphasized [[Nature (philosophy)|nature]] and related disciplines and therefore much of his thinking concerns living beings and their properties. The nature of universals in Aristotle's philosophy therefore hinges on his view of [[natural kind]]s. Instead of categorizing ''being'' according to the structure of thought, he proposed that the categorical analysis be directed upon the structure of the natural world.<ref>{{Cite book|last=Cocchiarella|first=Nino B.|title=Formal Ontology and Conceptual Realism|publisher=Springer Science & Business Media|year=2007|isbn=978-1-4020-6203-2|location=Dordrecht|pages=14}}</ref> He used the principle of [[Predication (philosophy)|predication]] in ''[[Categories (Aristotle)|Categories]]'', where he established that universal terms are involved in a relation of predication if some facts expressed by ordinary sentences hold.<ref>{{Cite book|last=Pinzani|first=Roberto|title=The Problem of Universals from Boethius to John of Salisbury|publisher=BRILL|year=2018|isbn=978-90-04-37114-9|location=Leiden|pages=2}}</ref>

In his work ''[[De Interpretatione|On Interpretation]]'', he maintained that the concept of "universal" is apt to be predicated of many and that singular is not.<ref>{{Cite book|last=Spade|first=Paul V.|title=Five Texts on the Mediaeval Problem of Universals: Porphyry, Boethius, Abelard, Duns Scotus, Ockham|publisher=Hackett Publishing|year=1994|isbn=087220250X|location=Indianapolis, Indiana|pages=x}}</ref> For instance, ''man'' is a universal while ''Callias'' is a singular. The philosopher distinguished highest genera like animal and species like man but he maintained that both are predicated of individual men.<ref name=":2">{{Cite book|last1=Berchman|first1=Robert|title=Studies on Plato, Aristotle and Proclus: The Collected Essays on Ancient Philosophy of John Cleary, Volume 15|last2=Finamore|first2=John|publisher=BRILL|year=2013|isbn=978-90-04-23323-2|location=Leiden|pages=364}}</ref> This was considered part of an approach to the principle of things, which adheres to the criterion that what is most universal is also most real.<ref name=":2" /> Consider for example a particular [[oak]] tree. This is a member of a species and it has much in common with other oak trees, past, [[present]] and future. Its universal, its oakness, is a part of it. A biologist can study oak trees and learn about oakness and more generally the intelligible order within the sensible world. Accordingly, Aristotle was more confident than Plato about coming to know the sensible world; he was a prototypical [[Empiricism|empiricist]] and a founder of [[Inductive reasoning|induction]]. Aristotle was a new, [[Moderate realism|moderate]] sort of realist about universals.