• Korean Journal of Logic
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• v.18 no.3
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• pp.337-358
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• 2015

Vann Mcgee produced "counterexamples" to Modus Ponens in "A Counterexample to Modus Ponens". Discussions about the examples tended to focus on a probabilistic reading of conditional statements. This article attempts to establish both (1) Modus Ponens is a deductively valid rule of inference, and (2) the counterexample-like appearance of Mcgee's example can be (and should be) explained without making a reference to the notion of conditional probability. The reason why his examples seem to counter Modus Ponens is found rather within the ambiguity a conditional statement exhibits. That is, Mcgee's examples are cases of equivocation on the conditional statements involved.

• Korean Journal of Logic
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• v.15 no.3
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• pp.323-347
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• 2012

After Byeongdeok Lee(2008) argued against the so-called uncontested principle (UP), Song(2008) and Choi(2011) gave arguments against Lee(2008) and instead for UP. One important point to mention in their arguments is that they all accept that UP is justifiable in deduction. First, I show that there are some problems in their arguments. Next, I show that UP itself is not justifiable in deduction; it is only justifiable under some (restrictive) conditions.