From Stephen's Guide (13)

flyingty · 发表于 2003-6-26 16:28:00

Non-Sequitur

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The term non sequitur literally means "it does not follow". In this section we
describe fallacies which occur as a consequence of invalid arguments.
The following fallacies are non sequiturs:

1. Affirming the Consequent

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Definition:

Any argument of the following form is invalid:
If A then B
B
Therefore, A

Examples:
(i) 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.)
(ii) 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

2. Denying the Antecedent

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Definition:

Any argument of the following form is invalid:
If A then B
Not A
Therefore, Not B

Examples:
(i) If you get hit by a car when you are six then you will die
young. But you were not hit by a car when you were six.
Thus you will not die young. (Of course, you could be hit by
a train at age seven, in which case you still die young.)
(ii) If I am in Calgary then I am in Alberta. I am not in
Calgary, thus, I am not in Alberta.

Proof:
Show that even though the premises are true, the conclusion
may be false. In particular, show that the consequence B may
occur even though A does not occur.

3. Inconsistency

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Definition:

The author asserts more than one proposition such that the
propositions cannot all be true. In such a case, the
propositions may be contradictories or they may be
contraries.

Examples:
(i) Montreal is about 200 km from Ottawa, while Toronto is
400 km from Ottawa. Toronto is closer to Ottawa than
Montreal.
(ii) John is taller than Jake, and Jake is taller than Fred,
while Fred is taller than John.

Proof:
Assume that one of the statements is true, and then use it as
a premise to show that one of the other statements is false

litoky · 发表于 2008-9-19 17:08:00

up

thanks for sharing

hoping useful

From Stephen's Guide (13)

From Stephen's Guide (13)

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