Модалната логика през Средновековието: Жан Буридан и видовете модалности.
Modal Logic in the Middle Ages: Jean Buridan and the Types of Modalities

Summary/Abstract: The aim of this article is to present John Buridan’ s understanding of modalities and modal proportions which has impact on nowadays research into the topic. For Buridan ‘possible’ and ‘necessary’ don’t include only actual things but also things that can be ‘that-and-that’. For him ‘S is possibly/ necessarily P’ means ‘This which is or can be S is possibly/ necessarily P’. This understanding of modalities is very close to modern theory of possible worlds and possible worlds semantics. However, it seems misleading to claim that Buri￾dan came up with an idea close enough to the concept of possible worlds or modern semantics. This understanding of modalities al￾lowed Buridan to make his famously octagon of opposition for de re modal propositions which is his main contribution to logic and philosophy. Buridan also introduced the rules for conversion for de re modal propositions which are the same as those for non-modal propositions but don’t hold for all of them. The article includes Buridan’s analysis of de dictum modal propositions and contingency. Although these two topics are not main research line nowadays, they are important to understand Buridan’s theory. Especially con￾tingency which does not have an equivalent in modern modal logic.

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