The Modal Fallacy is the best known of the fallacies related to Modal Logic. But, it is difficult to find the name of the logician who established the modal fallacy. Was it Aristotle? And, how does the classical Modal Fallacy differ from the more modern Modal Scope Fallacy?

  • Both fallacies you describe are specific to those who speak in terms of "modal logic" which means the terms are from the 20th century.
    – virmaior
    Jun 21, 2014 at 8:39

1 Answer 1


I'm not sure about this specific topic, i.e. the fallacy consisting in :

"interchanging" 'Nec(p -> q)' with 'p -> Nec q.'

But both modal logic and analysis of fallacies dates back to Aristotle : the second one in his De Sophisticis Elenchis (Sophistical Refutations), an appendix to the Topics.

The huge modern literature on Aristotle's syllogistics include :

A good discussion of Modal Theorem in Aristotle [if 'Nec(p)', and 'p -> q', then 'Nec(q)'] is in Jonathan Barnes, Truth etc Six Lectures on Ancient Logic, (2007), page 463-on.

A lot of useful material is discussed into Jonathan Barnes, Logical Matters Essays in Ancient Philosophy II (2012), Ch.3 : Logical form and logical matter (page 43-on), in particular the section on Necessity and syllogism (page 87-on) where we can find the material on the ancient debate regarding the relation between 'necessity' (the modal operator) and consequence (what is expresse in a valid argument by the word : 'therefore').


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