irvanellis
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to Logic-History-Research
In “On the Extension of the Common Logic”, The Journal of Philosophy,
Psychology and Scientific Methods 16 (1919), 379–383, Henry Bradford
Smith (1882–1938) wrote (p. 380) that:
‘“If Caesar be Socrates, then the moon is made of green cheese,” or
again, “If the moon be made of green cheese, then the angle-sum of the
triangle equals two right angles,” are applications of this extended
meaning which common sense accepts more readily than the cumbersome
mechanism of the ancient scheme of inference.’
Many of the more popular logic textbooks used in undergraduate
philosophy, whether dealing with Aristotelian syllogisms or classical
propositional calculus, use arguments which include as a premise “The
moon is made of green cheese” as an illustration of an argument which
is formally valid (but not sound), and as many who question material
implication in favor of strict implication (or some other alternative
to material implication) or the principle of Ex falso quodlibet in
general offer “The moon is made of green cheese” as an example of a
premise in arguments of questional validity.
My question is whether it is possible to identify the oldest, or one
of the oldest, logic textbooks that employ “The moon is made of green
cheese” as an example of an argument which is formally valid (but
unsound)? My guess is that we cannot go back much farther than the
late XVth century, since historical linguistics seems to suggest the
origin of that expression in print dates from the XVth century, found
in the Disciplina clericalis of Petrus Alphonsi (1062–1110?), which
exists in a XVth century English translation and was known to Chaucer.
In English, the expression occurs in John Heywood’s (ca. 1497–ca.
1580) book Proverbs of John Heywood (1546) and in Geoffrey Chaucer’s
(1340?–1400) “The Nun’s Priest’s Tale” from his Canterbury Tales, and
appears the works of Chaucer’s publisher, William Caxton (1422–1491),
himself the author of a logic, Mirrour of the World or the Tymage of
the Same (London; Westminster: W. Caxton, 1480; 1481); it appears in
the French Reynard the Fox fables. Does it appear in Caxton’s Mirrour?
If not, what is the earliest printed logic textbook in any language in
which this statement is given as an example of a false premise of a
valid argument?