• Source: Buridan formula

In quantified modal logic, the Buridan formula and the converse Buridan formula (more accurately, schemata rather than formulas) (i) syntactically state principles of interchange between quantifiers and modalities; (ii) semantically state a relation between domains of possible worlds. The formulas are named in honor of the medieval philosopher Jean Buridan by analogy with the Barcan formula and the converse Barcan formula introduced as axioms by Ruth Barcan Marcus.




The Buridan formula


The Buridan formula is:




◊
∀
x
F
x
→
∀
x
◊
F
x


{\displaystyle \Diamond \forall xFx\rightarrow \forall x\Diamond Fx}

.
In English, the schema reads: If possibly everything is F, then everything is possibly F. It is equivalent in a classical modal logic (but not necessarily in other formulations of modal logic) to




∃
x
◻
F
x
→
◻
∃
x
F
x


{\displaystyle \exists x\Box Fx\to \Box \exists xFx}

.




The converse Buridan formula


The converse Buridan formula is:




∀
x
◊
F
x
→
◊
∀
x
F
x


{\displaystyle \forall x\Diamond Fx\rightarrow \Diamond \forall xFx}

.




Buridan's logic


... As well as providing running commentaries on Aristotle's texts, Buridan wrote particularly influential question-commentaries, a typical genre of the medieval scholastic output, in which authors systematically discussed the most problematic issues raised by the text on which they were lecturing. The question-format allowed Buridan, using the conceptual tools he developed in his works on logic, to work out in detail his characteristically nominalist take on practically all aspects of Aristotelian philosophy. Among his logical works (which also comprise a number of important question-commentaries on Aristotle's logical writings), two stand out for their originality and significance: the short Treatise on Consequences, which provides a systematic account of Buridan's theory of inferences, and the much larger Summulae de Dialectica, Buridan's monumental work covering all aspects of his logical theory.
In medieval scholasticism, nominalists held that universals exist only subsequent to particular things or pragmatic circumstances, while realists followed Plato in asserting that universals exist independently of, and superior to, particular things.

... Buridan wrote his Summulae de Dialectica, which was to become the primary textbook of nominalist logic at European universities for about two centuries, in the form of a running commentary on the enormously influential logic tract of the venerable realist master, Peter of Spain. However, for the purposes of his commentary, Buridan completely reorganized Peter's treatise, and where Peter's realist doctrine went against his own nominalism, he simply replaced Peter's text with his own.




References



Anellis, I. H. (2007). "" Ibn-Sina's Anticipation of the Formulas of Buridan and Barcan," by Z. Movahed". The Review of Modern Logic. 11 (1–2): 73–86.
Richards, Jay W. (2009). The Untamed God: A Philosophical Exploration of Divine Perfection, Simplicity and Immutability. InterVarsity Press. p. 60. ISBN 9780830877430.
Besnard, P.; Guinnebault, J. M.; Mayer, E. (1997). "Propositional quantification for conditional logic". In Qualitative and Quantitative Practical Reasoning. Springer Berlin Heidelberg. pp. 183–197. See page 190.

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