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Affirming the Consequent
Definition:
Any argument of the following form is invalid:
If A then B
B
Therefore, A
Examples:
- If I am in Calgary, then I am in Alberta. I am in Alberta,
thus, I am in Calgary. (Of course, even though the premises
are true, I might be in Edmonton, Alberta.)
- If the mill were polluting the river then we would see an
increase in fish deaths. And fish deaths have increased. Thus,
the mill is polluting the river.
Proof:
Show that even though the premises are true, the conclusion
could be false. In general, show that B might be a
consequence of something other than A. For example, the fish
deaths might be caused by pesticide run-off, and not the mill.
References
Barker: 69, Cedarblom and Paulsen: 24, Copi and Cohen: 241
26 May 1995 / 06 January 1996
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