Talk:Hypothetical syllogism

message: There were no examples of counterfactual hypothetical syllogisms given in the section, but it sounded like what was being suggested is that hypothetical syllogism is valid even if all the conditionals are counterfactual conditionals.  But this is certainly not true, at least in standard systems of counterfactual logic, like David Lewis's.  If p is any contingently false proposition, these systems validate "if p were the case zero would still equal zero" and "if zero were equal to zero, p would still be false" but not "if p were the case, p would be false".  —Preceding unsigned comment added by 139.133.7.37 (talk) 15:01, 21 December 2009 (UTC)
thread_title:  deleted bit on how hypothetical syllogisms have the "advantage" that they can be counterfactual 

message: My logic study book explains hypothetical syllogisms as a category of syllogisms that contain a hypothetical proposition. It splits this up into three syllogisms: Conditionals (that which is described in this page), Disjunctives (described in the Disjunctive page), and Conjunctives (Both P and Q; Not P; Thus, not Q). But when I looked here to see what Wikipedia had to say about them, I saw Hypotheticals instead of Conditionals, and Disjunctives, but no Conjunctives. Some research affirms what I just said (here and here) while others call conditionals hypotheticals while still explaining all three together, as if there's some sort of category but completely unstated (here). Still others don't even mention Conjunctives on their websites (philosophy-index). Which is right? Should Wikipedia have an article on Conjunctive Syllogisms? There's woefully little information about Hypothetical Syllogisms.Whizzball1 (talk) 18:47, 17 November 2014 (UTC)
replies: text: The "Conjunctive" you describe is just wrong.  I believe the standard use of "Hypothetical Syllogism" dating back (more-or-less) to Aristotle is as described here, while the ones you describe are described here as modus ponens and disjunctive syllogism, while what you call "conjuctive", when corrected, follows from de Morgan's laws and disjunctive syllogism.  — Arthur Rubin  (talk) 10:37, 19 November 2014 (UTC)

text: I realised later that the Conjunctive I described there definitely is wrong. I believe now that what I mean is described on modus ponendo tollens: Not both P and Q. P. Thus, not Q. Sorry about the misunderstanding. Whizzball1 (talk) 19:01, 1 December 2014 (UTC)
thread_title:  Aren't hypothetical syllogisms a category of syllogisms rather than just a single type? 

message: In the introduction, it is written that the term "hypothetical syllogisms", was originated with Theophrastus. The reference is Britannica oline, but, at least at the time I am writing this comment, Britannica on line does not state exactly that. Here is an extract:
"Theophrastus is also credited with investigations into hypothetical syllogisms. A hypothetical proposition, for Theophrastus is a proposition made up of two or more component propositions (e.g., “p or q,” or “if p then q”), and a hypothetical syllogism is an inference containing at least one hypothetical proposition as a premise". 
Either Britannica is wrong here, or only the term "hypothetical proposition" goes with "for Theophrastus is a ...", while "hypothetical syllogism" was originated at a later time. 
And indeed, it was originated at a later time, according to Susanne Bobzien, professor of philosophy at Oxford University, in her article: "The Development of Modus Ponens in Antiquity: "From Aristotle to the 2nd Century AD", Phronesis, Vol. 47, No. 4 (2002), pp. 359-394: 
"In late antiquity, arguments of the ponens and tollens forms were generally classified as 'hypothetical syllogisms' (συλλογισμοὶ ὑποθετικοί, syllogismi hypothetici), and they were regarded as valid by virtue of these forms. However,as far as we know, Aristotle did not discuss such arguments, nor did he call any arguments 'hypothetical syllogisms'.
The Stoics, on the other hand, distinguished certain kinds of arguments that closely resemble modus ponens type argument. But they, too, did not call these arguments 'hypothetical syllogisms', nor did they describe them as ponendo ponens (i.e. as arguments that posit something by positing something), etc".
So, while Theophrastus and Eudemus were the first to investigate hypothetical syllogisms, the term was coined later. I proceed to make a correction.
 Aris Makridis (talk) 10:37, 2 November 2023 (UTC)
thread_title:  Error: "The term originated with Theophrastus"