William Ockham (1285-1349 AD), Walter Burley (1275–1344 AD), John Buridan (1301-1358 AD), and other medieval philosophers worked out many versions of the theory of supposition (reference):

• Propositions (sentences) are made up of terms.
• Terms in a proposition refer to other terms – the suppositum (or supposita); this relation is called supposition. The supposition of a term always occurs in a propositional context and can be entirely different from its signification (see [4.0.1]).
• Medieval philosophers elaborated complex categorizations for the relation of supposition. For example, Ockham and Burley, on the first level, divides suppositions into suppositions proper and improper.
• Proper suppositions for most authors on a second level are divided into the material, simple and personal. 
• More levels of different sub-divisions were elaborated by other medieval authors. 

The following OntoUML diagram pictures the main classes of the medieval theory of supposition.

Class	Description	Relations
Proposition	A proposition or sentence is made up of terms.
Term	A mental, spoken, or written term.	member of Propositon
Suppositum	Suppositum is “whatever a term supposits for” or refers to.	role of Term
Supposition	“What sort of relation is supposition? Well, the first thing we can say about it is that supposition is a semantic relation. To a first (but pretty good) approximation, supposition in this first part of the theory is what nowadays we call ‘reference.’ It is the relation between the terms used in a proposition and the things those terms are used to talk about in that proposition. […] supposition occurs only in a propositional context. And this is the first main difference between supposition and signification, which can occur outside a propositional context according to almost any author. The second main difference is this: We do not always in practice use terms in propositions to talk about what those terms signify. We use them in a variety of other ways too. Hence supposition also differs from signification insofar as a term may signify one thing, but supposit on a given occasion for something entirely different.”	relates Term, Suppositum and Proposition
ImproperSupposition	“Ockham describes the difference between the two near the very end of the first part of the Summa logicae: ‘Now you need to know that just as proper supposition occurs when a term supposits for what it properly signifies, improper supposition occurs when a term is employed improperly.’ This borders on tautology, and is not much help. As we shall see shortly, it is a very careless way of putting the matter. Burley’s way of stating the distinction is somewhat less precise, but at least not positively objectionable. Here is what he says in Purity, § 8: ‘By its first division, supposition is divided into proper and improper supposition. Supposition is proper when a term supposits for something for which it is permitted to supposit literally. Supposition is improper when a term supposits for something by transumption or from its usage in speech.’ Improper supposition therefore is the kind of supposition or reference a term has when it is used figuratively and not literally. Now a detailed semantics of metaphor was just as much beyond the reach of mediaeval authors as it is beyond our reach today. So we should not be surprised to find that the theory of improper supposition is not worked out very fully.”	subkind of Supposition
ProperSupposition	“proper supposition occurs when a term supposits for what it properly signifies“	subkind of Supposition
Material	Ockham defines it material supposition (Summa of Logic I.64, § 10) as follows: “Material supposition occurs when a term does not supposit significatively but supposits for an utterance or for an inscription. Notice that if the phrase ‘taken significatively’ does not mean what I have claimed it does, then on any other reasonable interpretation the term ‘utterance’ could never be in material supposition. As an example of material supposition, consider the proposition ‘Man is a monosyllable’. In the sense in which that proposition is true, the term ‘man’ supposits not for individual men, and not for the concept to which it is subordinated, but for itself. And, since it is not taken significatively there, it follows that the term is in material supposition.”	subkind of ProperSupposition
Simple	“Ockham defines simple supposition as follows (Summa of Logic I.64, § 8): Simple supposition occurs when a term supposits for an intention of the soul, but is not taken significatively. There’s that phrase ‘taken significatively’ again. Notice that if it does not mean what I think it does, then on the other interpretation the term ‘concept’ could never be in simple supposition. And that will turn out not to be so. Let me give you an example of the kind of thing Ockham has in mind for simple supposition. For Ockham, recall, there are no real universals or common natures. The only universals for him are universal concepts. And even they are not universal in the sense of being metaphysically shared by many things, as realists want universals to be. They are universal only in the sense that they are concepts of many things — they are “general” concepts. Metaphysically, they are just as individual as anything else; they are individual thoughts. They are not universal in the sense of being “in many”; they are universal only in the sense of being “predicated of many.” Ockham interprets talk about species and genera as referring to these general concepts, since they are the only plausible candidates, given his ontology. Hence for Ockham, in ‘Man is a species’, in the sense in which it is true, the subject term supposits not for some extramental universal or common nature that is the species, but rather for the concept of man, which is a specific concept. Now notice: In that proposition the term ‘man’ supposits for an intention of the soul, but it is not taken significatively, since it does not supposit for men there, but for the concept. Hence it is in simple supposition.”	subkind of ProperSupposition
Personal	Ockham defines personal supposition (Summa of Logic I.64, § 2) as follows: “Personal supposition, in general, is that [which occurs] when a term supposits for its significate, whether that significate is (a) a thing outside the soul, whether it is (b) an utterance, or (c) an intention of the soul, whether it is (d) an inscription, or anything else imaginable. So whenever the subject or predicate of a proposition supposits for its significate in such a way that it is taken significatively, the supposition is always personal. And he goes on to give some examples of the various possibilities he lists (ibid., §§ 3–6): (a) In ‘Every man is an animal’, ‘man’ supposits personally for a thing outside the soul. (b) In ‘Every spoken name is a part of speech’, ‘name’ supposits personally for utterances. (c) In ‘Every intention of the soul is in the soul’, ‘intention of the soul’ supposits personally for intentions of the soul. (d) In ‘Every written word is a word’, ‘written word’ supposits for inscriptions. In each case, the term refers to or supposits for the things it (primarily) signifies, the things it is truly predicable of, and so is in personal supposition. […] A term is taken significatively if and only if it is taken for (supposits for) everything it primarily signifies.”	subkind of ProperSupposition

Sources:

• All citations from: Spade, Vincent, “Thoughts, Words and Things: An Introduction to Late Mediaeval Logic and Semantic Theory”, Version 1.2: December 27, 2007
• Klima, Gyula, “John Buridan”, Oxford University Press, 2009
• Zupko, Jack, “John Buridan“, The Stanford Encyclopedia of Philosophy (Fall 2018 Edition), Edward N. Zalta (ed.)

First published: 26/8/2021