Chapter 10
Errors and Fallacies in Causal Reasoning
The Post Hoc Fallacy – this is sometimes called the post
hoc ergo propter hoc fallacy. The full phrase means:
“after this, therefore because of this” And it is a causal
inference fallacy. (304)
Just because one thing comes before another does not
mean that the first thing was causally relevant to the
second, and this is just what the post hoc fallacy claims.
It is classic bad reasoning.
The form of the post hoc fallacy can be expressed as
follows:
A occurred, then B occurred.
Therefore, A caused B.
OR
Events of type C happen immediately prior to events
of type E.
Therefore, events of type C cause events of type E.
When B is undesirable, this pattern is often extended
in reverse:
Avoiding A will prevent B.
The Post Hoc Fallacy is committed whenever one reasons to a
causal conclusion based solely on the supposed cause preceding its
"effect". Of course, it is a necessary condition of causation that the
cause precede the effect, but it is not a sufficient condition. Thus, post
hoc evidence may suggest the hypothesis of a causal relationship,
which then requires further testing, but it is never sufficient evidence
on its own.
Post Hoc also manifests itself as a bias towards jumping to
conclusions based upon coincidences. Superstition and magical
thinking include Post Hoc thinking; for instance, when a sick person is
treated by a witch doctor, or a faith healer, and becomes better
afterward, superstitious people conclude that the spell or prayer was
effective. Since most illnesses will go away on their own
eventually, any treatment will seem effective by Post Hoc thinking.
This is why it is so important to test proposed remedies carefully,
rather than jumping to conclusions based upon anecdotal evidence.
Examples of Post Hoc Fallacy
From Attacking Faulty Reasoning by T. Edward Damer:
"I can't help but think that you are the cause of this problem; we never
had any problem with the furnace until you moved into the apartment."
The manager of the apartment house, on no stated grounds other than
the temporal priority of the new tenant's occupancy, has that the
tenant's presence has some causal relationship to the furnace's
becoming faulty.
From With Good Reason by S. Morris Engel
More and more young people are attending high schools and colleges
today than ever before. Yet there is more juvenile delinquency and more
alienation among the young. This makes it clear that these young
people are being corrupted by their education.
Further Example of Post Hoc Fallacy
The only policy that effectively reduces public shootings is
right-to-carry laws. Allowing citizens to carry concealed
handguns reduces violent crime. In the 31 states that have
passed right-to-carry laws since the mid-1980s, the number
of multiple-victim public shootings and other violent crimes
has dropped dramatically. Murders fell by 7.65%, rapes by
5.2%, aggravated assaults by 7%, and robberies by 3%.
Chapter 10
The fallacy of objectionable cause: occurs when a person
argues for a causal interpretation on the basis of limited
evidence and makes no attempt to rule out alternative
explanations of the event. (306)
Sometimes this fallacy is called the false cause fallacy.
This kind of fallacy happens a lot in election debates and it
is similar to a confusion of correlation with causation.
This fallacy has the following general form:
A and B are associated on a regular basis.
Therefore A is the cause of B.
The general idea behind this fallacy is that it is an error in
reasoning to conclude that one thing causes another simply
because the two are associated on a regular basis.
More formally, this fallacy is committed when it is concluded that A
is the cause of B simply because they are associated on a regular
basis. The error being made is that a causal conclusion is being
drawn from inadequate evidence.
The Questionable Cause Fallacy is actually a general type of
fallacy. Any causal fallacy that involves an error in a reasoning due
to a failure to adequately investigate the suspected cause is a
fallacy of this type.
Examples of Objectionable Cause:
"Defense attorney Ellis Rubin claims Ronald Zamora's constant exposure to TV
crime shows such as re-runs of 'Kojak' and 'Police Woman' was responsible for
'diseasing his mind and impairing his behavior controls.' 'Without the influence
of television ... there would not have been any crime,' Rubin argued." Index
Journal
When investigating a small pond a group of graduate students found that there
was a severe drop in the fish population. Further investigation revealed that the
fishes' food supply had also been severely reduced. At first the students
believed that the lack of food was killing the fish, but then they realized they had
to find what was causing the decline in the food supply. The students suspected
acid rain was the cause of both the reduction in the fish population as well as
the food supply. However, the local business council insisted that it was just the
lack of food that caused the reduction in the fish population. Most of the
townspeople agreed with this conclusion since it seemed pretty obvious that a
lack of food would cause fish to die.
Chapter 10
Begging the Question in a Causal Account:
This is just a case of begging the question in a situation
where there is some causal claim our account in
question. So, a person assumes the conclusion or
something logical equivalent to the causal conclusion as
support for it.
See page 308 for a detailed example.
Chapter 10
Causal Slippery Slope Arguments:
Causal Slippery Slope fallacy claims in the premises that
some action would be wrong because it would let off a
series of side effects ending ultimately in general
calamity.
Causal slippery slope fallacies can also go in the other
direction claiming that something would be good
because it would give rise to certain good effects.
Fixing these fallacious arguments generally requires
providing cogent subarguments for the premises.
The General Pattern of Slippery Slope
If A happens, then by a gradual series of small
steps through B, C,…, X, Y, eventually Z will
happen, too.
Z should not happen.
Therefore, A should not happen, either.
Example of Slippery Slope
If today you can take a thing like evolution and make it a crime to teach it in
the public school, tomorrow you can make it a crime to teach it in the private
schools, and the next year you can make it a crime to teach it to the
hustings or in the church. At the next session you may ban books and the
newspapers. Soon you may set Catholic against Protestant and Protestant
against Protestant, and try to foist your own religion upon the minds of men.
If you can do one you can do the other. Ignorance and fanaticism is ever
busy and needs feeding. Always it is feeding and gloating for more. Today it
is the public school teachers, tomorrow the private. The next day the
preachers and the lectures, the magazines, the books, the newspapers.
After [a]while, your honor, it is the setting of man against man and creed
against creed until with flying banners and beating drums we are marching
backward to the glorious ages of the sixteenth century when bigots lighted
fagots to burn the men who dared to bring any intelligence and
enlightenment and culture to the human mind.
Source: Clarence Darrow, The Scopes Trial, Day 2