[4.9.8] St Thomas Aquinas on Universals

St Thomas Aquinas (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 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 [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.
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.”

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

[4.5.2] Gilbert of Poitiers on Universals

Gilbert of Poitiers (Gilbert de la Porrée, 1085?–1154 AD) in different commentaries to Boethius’s De Trinitate, De Hebdomadibus, and Contra Eutychen et Nestorium proposes an anti-realist theory of universals, according to which:

  • universals (like genus and species) are sets (collectiones)
  • these sets are based on the resemblance of some essential properties (subsistentiae) of individuals.

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

Porphyry’s questionsUniversals according to Gilbert
(a) whether genera and species [universals] are real or are situated in bare thoughts aloneare situated in thoughts (as sets)
(b) whether as real they are bodies or incorporealsthey are not real things
(c) whether they are separated or in sensibles and have their reality in connection with themthey are not real things

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

Gilbert of Poitiers on universals
GenusGenus is a collection of Species
SpeciesSpecies is a collection of EssientialProperites (substancia), based on their resemblance (Conformitas)is subcollection of Genus
Conformitas“For Gilbert, a universal is a collection of properties on the basis of resemblance. His theory is based upon the notion of conformitas. There are many subsistentiae of a given kind, the number of which is the same as that of the subsistents of which they are the being (this thesis is summarized clearly by the author of the Compendium Logicae Porretanum in the formula ‘there are as many humanities as there are men’), and their natural conformity causes their generic or specific union. Gilbert notes that universals are ‘collected from particulars by the intellect.’ The intellect is able to abstract on the basis of conformitas, which is naturally given and may be observed through the manifest resemblance that exists between things in the sensible world. The universal is the union of subsistentiae in virtue of their conformity—union, but not unity.”mediates between EssentialProperies; Species is abstracted (by the Intellect) form Conformitas
Essential Property“An id quo —that is, an essential property—is also called subsistentia, a particular essential property or substantial form determining the being of just one individual. Each individual, or subsistens, is constituted of several subsistentiae. The interest and originality of Gilbert’s position lie in the fact that each of these subsistentiae is particular.”
E.g. The animality of Felix, the cat.
component of Essence
Essence“All these subsistentiae taken together constitute the essence of an individual, which Gilbert calls tota substantia.component of TotalForm
TotalForm“Gilbert offers a very interesting theoretical tool for the consideration of an individual seen over a whole lifetime. He probably pursues the doctrinal aim of ensuring personal identity across time and of avoiding that an individual undergoing qualitative or quantitative change becomes a different individual. Gilbert introduces the concept of forma tota [total form] to refer to the set of all the properties that might be true of a given subject, including also those that will never be actualized. The sum of the essential properties and accidents thus constitutes the forma tota of the individual; the sum of the characteristics of Socrates is called Socrateitas and the sum of those of Plato, Platonitas. According to Gilbert, the tota forma of an individual—for example, Plato’s Platonitas— includes all its subsistences (its substantia tota) but also its quantitative and qualitative accidents—not only those it possesses actually (actu), but also those it possessed in the past and those it will or could possess in future according to the potentiality of its own nature. Expressed as bundle, the forma tota could be understood as the most comprehensive possible bundle. This total form belongs to just one concrete being. The individuality of a concrete being or, in Gilbert’s words, its numerical diversity, is caused by the particularity of its essential properties and rendered manifest by the fact that it possesses its own total form. An anonymous Porretan treatise is explicit when it speaks of the case of the individual Peter. The form which is composed of all the various properties, both essential and accidental, which are in Peter, and which make Peter different from all the other men, is called petritas. This form is particular, and explains how Peter is a being discrete from all other men”.characterizes Individual
Individual“An id quod est is an independent individual, such as Peter, my cat Felix, or this apple. Gilbert uses an alternative terminology: an id quod est, an individual, is also called a subsistens, a subsisting entity. […]
An individual is the sum, the collection of all its essential subsistentiae and particular accidental properties.”

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], [4.4.1][4.5.2], [4.9.8]


  • All citations from: Erismann, Christophe, “Explaining Exact Resemblance: Gilbert of Poitiers’s Conformitas Theory Reconsidered”, Oxford Studies in Medieval Philosophy, Volume 2, Edited by ROBERT PASNAU,2014
  • Adamson, Peter, “216. One of a Kind: Gilbert of Poitiers on Individuation“, History of Philosophy without any Gaps podcast

First published: 07/07/2020