Phil. 103: Introduction to Logic
Class Exercise: Fallacies of Presumption Answers
Version 1.1 c
2008 GFDL
Directions : Identify the informal fallacies in the following passages. Choose
from the fallacies of complex question, false cause, petitio principii, accident,
and converse accident.
1. Studying a sub ject too much and in too much depth is often confusing
for the reason that when you study so much and so intensively the main
points of the subject are no longer clear.
petitio principii. The premiss and the conclusion of this argument
are logically equivalent, so no supporting reasons are being offered
for the conclusion.
2. Studies have shown that people who attend sports events regularly suffer
more cardiac arrests on the average than those people who do not attend
regularly. Thus, we can confidently conclude that regular attendance at
sports events is a important factor producing poor cardiac health.
false cause. (post hoc ergo propter hoc ). The argument states
that attendance at sports events are often occasioned by persons
suffering cardiac arrests, so the attendance is the cause of heart
trouble. One event following another is not a sufficient reason
to conclude that the first event caused the second to occur.
3. Even though Bob Smith worked long and hard hours on the corporate
summer progress report, the chairman of the finance committee showed
that Smith’s efforts amounted to a superficial presentation. It’s obvious
that Bob just can’t be relied upon to produce adequate rep orts.
converse accident. Simply because one person concludes that Smith’s
report was inadequate, it cannot be logically concluded that all
of his writing would be substandard.
4. How can the nation cover rising health care costs, pass legislation for lower
taxes for our citizens, support our armed forces for a strong national de-
fense, protect the farmer from high interest rates and rising fuel costs,
and simplify the bewildering array of interstate commerce laws? It’s obvi-
ous that major the political parties can’t do this—there’s only one viable
solution, vote Independent in the next election.
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