[4.9.8] St Thomas Aquinas on Universals

St Thomas Aquinas ( “Doctor Angelicus”, 1225 – 1274 AD), in his short treatise On Being and Essence, explains his moderate theory of universals:

  • Each singular being has its own unique nature (or essence, see also [4.9.2][4.9.3]). These natures are alike for the beings belonging to the same universal (like genus, species).
  • This likeness, sameness (or analogy) can be recognized, and as such, abstracted in the mind. The natures abstracted in the mind are universal concepts.
  • Aquinas’s moderately realistic model solves the “epistemological problem of the possibility of universal knowledge, without entailing the ontological problems of naïve Platonism.”

Here are Aquinas’s responses to Porphyry’s questions (see [2.5]):

Porphyry’s questionsUniversals according to Aquinas
(a) whether genera and species are real or are situated in bare thoughts alonethey are real
(b) whether as real they are bodies or incorporealsthey are incorporeals
(c) whether they are separated or in sensibles and have their reality in connection with themthey have reality connected to sensibles (singular objects)

Aquinas’s model of universals is pictured in the following OntoUML diagram:

Aquinas on universals
Nature“a common nature or essence according to its absolute consideration abstracts from all existence, both in the singulars and in the mind. Yet, and this is the important point, it is the same nature that informs both the singulars that have this nature and the minds conceiving of them in terms of this nature.”
NatureInSingularNature abstracted in the singular being.subkind of Nature; exlusive part of SingularBeing; in natural relation with NatureInMind
NatureInMindNature abstracted in the singular (a human person’s) mind.subkind of Nature; exlusive part of SingularMind; is UniversalConcept
Sameness“To be sure, this sameness [or analogy of nature in the singular and in the mind] is not numerical sameness, and thus it does not yield numerically one nature [essence]. On the contrary, it is the sameness of several, numerically distinct realizations of the same information-content, just like the sameness of a book in its several copies. Just as there is no such a thing as a universal book over and above the singular copies of the same book, so there is no such a thing as a universal nature existing over and above the singular things of the same nature; still, just as it is true to say that the singular copies are the copies of the same book, so it is true to say that these singulars are of the same nature. […] this common nature is recognizably the same on account of disregarding its individuating conditions in the singulars”relates NatureInSingular with NatureInMind
SingularBeingA singular being is a particular thing.contains Matter
SingularMindA singular mind is a human person’s mind.
UniversalConcept“using our analogy, we can certainly consistently say that the same book in its first edition was 200 pages, whereas in the second only 100, because it was printed on larger pages, but the book itself, as such, is neither 200 nor 100 pages, although it can be either. In the same way, we can consistently say that the same nature as such is neither in the singulars nor in the mind, but of course it is only insofar as it is in the mind that it can be recognizably the same, on account of the mind’s abstraction. Therefore, that it is abstract and is actually recognized as the same in its many instances is something that belongs to the same nature only on account of being conceived by the abstractive mind. This is the reason why the nature is called a universal concept, insofar as it is in the mind. Indeed, it is only under this aspect that it is properly called a universal. So, although that which is predicable of several singulars is nothing but the common nature as such, considered absolutely, still, that it is predicable pertains to the same nature only on account of being conceived by the abstractive intellect, insofar as it is a concept of the mind.”
MatterMatter individuates singular being. individuates SingularBeing

Related posts in theory of Universals: [1.2.2][1.3.1][1.3.2][2.5][2.7.3][4.3.1][4.3.2][4.4.1], [4.5.2], [4.9.8]


  • All citations from: Klima, Gyula, “The Medieval Problem of Universals”The Stanford Encyclopedia of Philosophy (Winter 2017 Edition), Edward N. Zalta (ed.)
  • The Cambridge Companion to Aquinas, CAMBRIDGE UNIVERSITY PRESS, Edited by  Norman Kretzmann and Eleonore Stump, 2010
  • McInerny, Ralph and John O’Callaghan, “Saint Thomas Aquinas”The Stanford Encyclopedia of Philosophy (Summer 2018 Edition), Edward N. Zalta (ed.)

First published: 29/10/2020
Updated: 2/5/2021 Added matter and individuation.

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