Informal Logic, 14, 123-130 (1992)
Informal logicians recognise the frequent use of unstated
assumptions; some (e.g. Fisher) also recognise entertained
arguments and recommend a suppositional approach (such as
Mackie's) to conditional statements. It is here argued that
these two be put together to make argument diagrams more accurate
and subtle. Philosophical benefits also accrue: insights
into Jackson's apparent violations of modus tollens and
contraposition and McGee's counterexamples to the validity of
modus ponens.
Key Words:
argument analysis
conditionals
Fisher
Jackson
Mackie
McGee
supposition
unstated premises
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