PHL 3000 Lecture Notes - Lecture 4: Formal Fallacy, Informal Fallacy, Logical Form
Module 4
Lecture 4.1: Fallacies
What is a Fallacy?
• Fallacies are mistakes in reasoning that are so common that we have given them names
o Formal fallacies are mistakes in reasoning that depend on the logical structure of
the argument
o Informal fallacies are mistakes in reasoning that depend on the content, or
language used in the argument
Formal Fallacies
• Example of formal fallacy:
o If cultural relativism is correct (A), then we should be tolerant of other cultures
and their moral beliefs (B)
o We should be tolerant of other cultures and their moral beliefs
o Therefore, cultural relativism is correct
▪ If A is true then B is true.
▪ B is true
▪ Therefore A is true
o If it is raining, then the streets are wet
▪ true
o The streets are wet
▪ true
o Therefore, it is raining
▪ The streets could be wet for a variety of reasons
• This was an example of a formal fallacy: the problem with this line of reasoning is that
this structure, or way of reasoning, doesn’t guarantee the truth of the conclusion,
regardless of what is being discussed
o If A then B. B. Therefore A. – does not work
• It is the argument form that is at fault here, hence formal fallacy.
Informal Fallacies
• Example of informal fallacy:
o Every member of the team plays the game very well
o Therefore, the team as a whole plays the game very well
▪ This doesn’t always follow: sometimes, too many stars make a team play
poorly rather than well
▪ Just because the parts are good doesn’t mean the whole is good
• However this is not a formal fallacy, which you can tell by considering another argument:
o Every part of this blanket is red.
o Therefore, the blanket itself is red
• The difference between the arguments is blankets and teams have different natures.
Arguing form part to whole can work for blankets but not for teams.
o Sometimes arguing from part to whole is fallacious (good players = good team)
o Sometimes it is not fallacious (red parts to blanket = red blanket)
• We cannot just examine the form of the argument, but must ask about the content,
making this an informal fallacy.
Reasons to Study Fallacies
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• Most important reason: identify and avoid them in your own thinking
• Another reason: identify them in the reasoning of others
o However don’t be too quick to accuse someone of committing a fallacy
o Always try to interpret others in as strong a way as possible (principle of
charity)
Lecture 4.2: Fallacies of Relevance
Fallacies of Relevance
• Fallacies of relevance are fallacies in which the premises of the argument are logically
irrelevant to the conclusion
o These are all examples of informal fallacies, since the question of whether a
premise is relevant to the conclusion depends of the meaning of the conclusion
and the premises (the content)
Appeal to Force
• The fallacy of appeal to force occurs whenever someone argues that a conclusion should
be accepted due to a threat of physical or psychological harm
o If I don’t pass this class, we could have a serious problem, professor
o If you don’t change my grade, I will sue you for loss of future earnings
▪ The only relevant issue to your grade is your performance
Appeal to Pity
• The fallacy of appeal to pity occurs when the arguer attempts to support a conclusion
simply by eliciting a feeling of pity in the listener.
o If you fail me for the course, I will lose my scholarship
▪ Again the only relevant issue to your grade is your performance
• However, sometimes an argument might make you feel pity towards someone without
being fallacious
o Veal calves live in utter misery for their short lives
o The benefits we receive from treating veal calves this way is very slight
o Therefore, we should not treat veal calves this way
▪ Premise is relevant to the conclusion
▪ Ask: is the fact that this is causing me to feel pity relevant to the
conclusion?
• No general rules that can be used here, but you must instead use your best judgment to
determine whether the premises are relevant to the conclusion
Appeal to the People
• The fallacy of appeal to the people occurs whenever someone supports a conclusion by
pointing out that some segment of people accept that conclusion as well, and that group
has no particular expertise concerning the conclusion
o Normally an appeal to our vanity, ego, or need to fit in
• There are many different versions, however in general it is supporting a conclusion by
appealing to the beliefs/activities of non-experts
• Example 1:
o Everyone is saying GMOs are bad
o Therefore GMOs are bad
• Example 2:
o Rolex watches are not for everyone, but only for those with taste
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o You clearly have taste
o Therefore, Rolex watches are for you
▪ Appealing to your vanity
• We can believe what we do because of expert testimonials. They have to be experts
though
Argument Against the Person
• The fallacy of argument against the person occurs whenever someone responds to the
reasoning of another by ignoring the content of what was said, and focuses instead on
the person who said it
o Person A: Eating meat is wrong because raising animals for food causes them
so much pain
o Person B: Then why are you wearing leather?
• Some forms of this fallacy involve attacking the speaker’s character as a way of
rejecting their beliefs
o Nietzsche argues that traditional morality undermines what is truly valuable,
but he was an atheistic degenerate who went insane. We can ignore whatever
he said.
• It is not always fallacious to conclude that someone is a bad person, or liar.
o Bob lies to people very often
o Therefore, Bob is a liar
▪ Not fallacious, just applying the definition of liar to Bob
• It is not fallacious to question whether someone’s statements or beliefs are being
influenced by their self-interest:
o The coal industry claims that coal is clean, but since they have so much to
gain from people believing this, we should not accept it without further
scrutiny
The Accident Fallacy
• The accident fallacy occurs whenever someone applies a general rule to a situation that
the rule was not meant to cover
o That ambulance driver should be fired, since the speed limit is 65 and he is going
over it
▪ Obviously ambulance drivers can break the speed limit
o Since you promised to help me yesterday, you must now do what I ask, and I want
you to help me rob a store
▪ They are asking you to do something morally wrong
The Red Herring Fallacy
• The red herring fallacy occurs whenever someone changes the subject in the middle of an
argument, often in a subtle way
o Some people say there should be tougher laws on guns. But crime is running out
of control and there is so much violence in poorer neighborhoods. There really
needs to be some kind of change in society if this is to improve.
Lecture 4.3: Fallacies of Weak Induction
Fallacies of Weak Induction
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Document Summary
It is the argument form that is at fault here, hence formal fallacy. It is not always fallacious to conclude that someone is a bad person, or liar: bob lies to people very often, therefore, bob is a liar, not fallacious, just applying the definition of liar to bob. The red herring fallacy: the red herring fallacy occurs whenever someone changes the subject in the middle of an argument, often in a subtle way, some people say there should be tougher laws on guns. But crime is running out of control and there is so much violence in poorer neighborhoods. There really needs to be some kind of change in society if this is to improve. Likewise, no one should get married without first having had sex with their partner: there may be truth in both statements but they have nothing to do with each other. Lecture 4. 4: fallacies of presumption, ambiguity, & illicit transfer.
