supposition

logic

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July 14, 2026

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Supposition, in logic, refers to an idea or assumption used as a starting point for an argument or investigation. This concept was central to medieval logic, particularly in the theory of supposition, which explored how terms in a proposition refer to things.12

There are different types of supposition:
* Personal supposition: The term refers to individual instances (e.g., "Every horse is an animal").
* Simple supposition: The term refers to a universal concept (e.g., "Horse is a species").
* Material supposition: The term refers to the word itself (e.g., "Horse is a monosyllable").

Further distinctions were made within personal supposition, such as determinate, confused, and distributive types, aiding in the analysis of propositions and potentially detecting fallacies. The theory of supposition was a key tool for semantic analysis throughout the Middle Ages and continued to influence logic, theology, and science.2

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history of logic
The theory of supposition
Many of the characteristically medieval logical doctrines in the Logica moderna centred on the notion of “supposition” (suppositio). Already by the late 12th century, the theory of supposition had begun to form. In the 13th century, special treatises on the topic multiplied. The summulists…
Read More
Many of the characteristically medieval logical doctrines in the Logica moderna centred on the notion of “supposition” (suppositio). Already by the late 12th century, the theory of supposition had begun to form. In the 13th century, special treatises on the topic multiplied. The summulists…
Read More