From The Logic Museum
In scholastic logic supposition is a relation between a term, and the objects which it ultimately signifies. It is analogous to the concept of reference in modern philosophical logic, except that it is a property of common terms as well as singular terms, rather than of singular terms alone. There are various subdivisions or kinds of supposition, of which the most significant is ‘personal’ supposition, the relation between a common term like ‘man’ and all men, or between a proper name like ‘Socrates’ and the individual it refers to (Socrates).
Supposition theory originated in the medieval Latin West. Its early development, probably in the second half of the twelfth century, is mysterious. It came to prominence in the latter half of the thirteenth century, and a version of it is the basis of William of Ockham’s nominalism, set out in his Summa Logicae.
Signification and supposition
Lambert of Auxerre says that signification is prior to supposition. He says that signification is the concept represented by an utterance (vox) whereas supposition is a property of a term, which is the result of concept and utterance. Another difference is that signification extends only to the 'thing' (res) the term is imposed to signify, whereas supposition extends to the things contained under that thing. For example, the utterance 'man' signifies man, but supposits for Socrates, Plato etc. Jean Buridan says that a word signifies a concept in the hearer, whereas a term supposits when it is predicable of the pronoun 'this', and the pronoun points out something. Thus 'chimera' cannot supposit, since it is always false to say 'this is a chimera'.
Kinds of supposition
There are various kinds of supposition.
- Improper and proper. Improper supposition is when an utterance supposits according to the signification of another utterance, as in analogy (such as when we say that a storm is angry, or that someone is a lion) or irony (“he has married a treasure”). Proper supposition is when an utterance supposits according to to the signification that is imposed on it in common usage.
- Personal, material and simple. Personal supposition is when the subject or the predicate of a proposition supposits for its ‘ultimate significates’. For example, when the term ‘man’ supposits for any man in the proposition ‘a man runs’. Material supposition is when an utterance supposits for itself. Some authors mention a third kind of proper supposition, namely simple supposition. This is when a term stands for a common or universal nature or (according to writers such as Ockham) when it stands for a universal concept. According to the first, the term man in the proposition ‘man is a species’ stands for a common nature or universal. According to the second, it stands for a concept or ‘intention of the soul’. Buridan classifies simple supposition as a form of material supposition.
- Common and discrete. Common supposition is when a term naturally supposits for more than one thing, such as the term 'man' standing for all men, however many there are. Discrete supposition is when the term naturally stands for just one thing, such as 'Socrates' or 'this man'.
- Natural and accidental. Parisian writers of the early thirteenth century considered supposition to be 'natural' when a term stands for every thing which it can possibly stand for (e.g. when 'man' naturally stands for past, present or future men), but 'accidental' when it stands for things by contextually determined features such as the tense of the verb, or the predicate. By contrast, both the Fallaciae Parvipontanae and early Oxford texts consider past and future tense verbs as ampliating verbs like 'can'. Some authors of the late 13th century also deny the concept of natural supposition in this sense. 
- Confused and determinate. This is usually a division of personal supposition. Supposition is determinate when the proposition has to be verified by some determinate individual, i.e. we can ‘descend to singulars’ by a disjunction. For example, the proposition ‘a man is running’ is true if the man Socrates is running, or Plato is running, or Aristotle is running, and so on ‘for all the singulars’. Otherwise it is confused.
Division of supposition
Whereas most scholastic writers on the subject agreed on the basic types of supposition, they did not agree on their relative subdivisions. Peter of Spain divides supposition into discrete and common, common supposition into natural and accidental, accidental common supposition into simple and personal. Lambert of Auxerre makes natural/accidental a primary division of supposition. William of Ockham makes common and discrete a division of personal supposition only. William of Sherwood divides formal supposition into common and discrete, and into simple and personal, thus allowing for discrete-simple supposition. To the objection that discrete supposition can only be personal – since a particular individual is always supposited for – he replies that it is not the fact that an individual is supposited for that makes personal supposition, but the fact that "a thing bearing the form signified by the name is supposited". When we say "Socrates is predicable of one person only", this is with respect to the form signified by the name 'Socrates'.
Simple supposition was originally when a term stands for a nature or essence, rather than when it stands for the thing having that nature or essence. John of Salisbury says that our understanding sometimes looks directly at the simple essence of things without composition, such as when it conceives of a man per se or a stone per se, although he does mention it in the context of supposition. William of Sherwood says that supposition is simple when a word supposits its significate for a significate (supponit significatum pro significato), such as when we say "man is a species".
Lambert says that simple supposition is when a term holds for its [signified] thing (pro re sua), and not in respect of the supposita contained under it. It is called simple because it is in the term by reason of form, and a form is simple and indivisible, according to the book of six principles.
William of Ockham, on the other hand, says that simple supposition is when when a term supposits for a mental concept or 'intention of the soul'. For example, in saying ‘Man is a species’, the term ‘man’ supposits for an intention of the soul. This is consistent with his nominalism, according to which common nouns do not signify extra-mental natures or essences, but rather intra-mental concepts or 'intentions'. He rejects the opinion of the earlier writers:
- From this is clear the falsity of the opinion of those commonly saying that simple supposition is when a term supposits for its significate (pro suo significato), because simple supposition is when a term supposits for an intention of the soul that is not properly a significate of the term. For such a term signifies true things and not intentions of the soul.
Buridan mentions both views. Those who believed that there are universal natures distinct from the soul and from singulars, said that a term supposits simply when it supposits for a universal nature. Others (meaning Ockham, presumably) say that supposition is simple when it supposits for the concept for which it is imposed. He rejects the first view, believing that Aristotle rejected it in the seventh book of the Metaphysics.
- ↑ Kneale & Kneale 1962 IV. 4, p.246. See also Joseph P. Mulally, The Summulae Logicales of Peter of Spain, Publications in Medieval Studies, vol. 8, Notre-Dame 1945 pp. xxxviii et seq
- ↑ Summalae de dialectica, 4. 1. 1.
- ↑ See Thomas Aquinas Summa Theologiae ST I Q13 a6 contra, also Buridan, Summulae de dialectica IV 3.1
- ↑ Summa Logicae Part I chapter 68
- ↑ Summulae_de_dialectica Book 4 c. 3
- ↑ CHLMP chapter 8 "The Oxford and Paris traditions in logic" p.174
- ↑ Summulae Logicales, ed. Bochenski p. 58
- ↑ Kretzmann p. 110
- ↑ Metalogicon 2.20
- ↑ Liber de sex principiis Gilberto Porretae ascriptus (ed. Heysse-van den Eynde) I, 1, (p. 8).
- ↑ Summar Logicae I 64
- ↑ Ibid
- ↑ Summulae Dialectica 4.3.2