Name: __________________________________________ Class Period: ________________
Identifying Faulty Reasoning – Practice
In each of these cases, determine whether the reasoning is sound. If the conclusions are not
supported by the data, determine what type of faulty reasoning led to the conclusion.
My town needs a new place to dispose of garbage, because the current
landfill is almost full. The engineers who are designing the new landfill think that it
should be located on the west side of town because (1) the soil is more stable
and (2) there is a stream on the east side of town that could become
contaminated. I disagree with them. I think that the landfill should be located on
the east side. I have several very good reasons. First, the people on the west
side of town, including me, don’t want to live near the dump. Second, the stream
is already contaminated, so it won’t matter if a bit more contamination gets into it.
Third, it really doesn’t matter about soil stability because there are ways to make
the dump safe even if the soil is unstable.
1. Are these arguments sound? Why or why not? Give specific examples. If not, what type of
faulty reasoning is used?
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Scientists have been tracking water and wind currents. They have
determined that warming water causes changes in these currents. They have
recorded and compared Pacific water temperatures and North American weather
data for several decades. Additional data from studies of sediments and tree
rings indicate that the effect has existed for many centuries.
One conclusion from these studies is that warm water at the surface of the
ocean off the coast of South America can cause the weather in the northeastern
United States to become warmer and drier than normal.
2. Is this conclusion sound? Why or why not? Give specific examples. If not, what type of
faulty reasoning is used?
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You should always avoid walking
under a ladder because it brings bad luck.
Yesterday, I was cleaning windows and
walked underneath a ladder. Later in the
day, I spilled milk on the living room carpet.
Then I lost my homework and had to start
over. As I was starting to work again, the
bulb in my reading lamp burned out. You can
be sure that I won’t walk under ladders
again.
3. Are these good reasons to not walk under ladders? Why or why not? Give specific
examples. If not, what type of faulty reasoning is used?
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Fish live and swim in the ocean. They have fins and long streamlined
bodies. Many kinds of fish eat smaller fish and other animals. Because this
description applies to all of the animals in the illustration, they can all be
classified as fish.
4. Is this an example of sound reasoning? Why or why not? Give specific examples. If not,
what type of faulty reasoning is used?
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