The current meanings arose from the equation of medieval Latin suppositio to Greek ὑπόθεσιςhypothesis n., of which it is the etymological equivalent. In older Latin suppositio is recorded only in the senses of ‘placing under’ and ‘substitution’
- 1: Something held to be true and taken as the basis of an argument.
- 2: a. The action of assuming, or, usually, that which is assumed (which may be either true or false), as a basis of argument or a premiss from which a conclusion is drawn.
- 3: a. A notion or idea that the thing in question is true, held without certainty or assurance, but as sufficiently probable to be assumed or admitted on account of agreement with the facts of the case; a hypothetical inference, or the action of making such inferences; an uncertain (sometimes, by implication, a false or mistaken) belief. †in supposition, in uncertainty, uncertain, doubtful
- b. Used vaguely, with various shades of meaning: Idea, notion; imagination, fancy; occas. suspicion, expectation.
- b. Insertion of something not genuine in a writing; that which is so inserted, an interpolation, a spurious passage; a spurious writing, a forgery.
Supposition was a semantic relation between a term and what it is being used to talk about. So, for example, in the suggestion Drink another cup the term cup is suppositing for the wine contained in the cup. The logical suppositum of a term was the object the term referred to, (in grammar suppositum was used in a different way). However, supposition was a different semantic relationship than signification. Signification was a conventional relationship between utterances and objects mediated by the particularities of a language. Poculum signifies in Latin, what cup signifies in English. Signification is the imposition of a meaning on an utterance, but supposition is taking a meaningful term as standing in for something. According to Peter of Spain "Hence signification is prior to supposition. Neither do they belong to the same thing. For to signify belongs to an utterance, but to supposit belongs to a term already, as it were, put together out of an utterance and a signification." An easy way to see the difference is in our drink another cup example. Here cup as an utterance signifies a cup as an object, but cup as a term of the language English is being used to supposit for the wine contained in the cup.
Medieval logicians divided supposition into many different kinds, and the jargons for the different kinds, and their relations and what they all mean get complex, and differ greatly from logician to logician. Paul Spade's webpage has a series of helpful diagrams here. The most important division is probably between material, simple, personal, and improper supposition. A term supposits materially, when it is used to stand in for an utterance or inscription, rather than for what is signifies. When I say Cup is a monosyllabic word, I am using the word cup to supposit materially for the utterance cup rather than for a piece of pottery. Material supposition is a medieval way of doing the work we would do today by using quotation marks. According to Ockham (Summa of Logic I64, 8) "Simple supposition occurs when a term supposits for an intention of the soul, but is not take significatively." The idea is that simple signification happens when the term is standing in for a human concept rather than for the object itself. If I say Cups are an important type of pottery the term cups is not standing in for any particular cup, but for the idea of a cup in the human mind (according to Ockham, and many medieval logicians. Personal supposition in contrast is when the term supposits for what is signifies. If I say Pass me the cup the term cup is standing in for the object that is called a cup in English, so it is in personal supposition. A term is in improper supposition, if it is suppositing for an object, but a different object than it signifies, as in my example Drink another cup.