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Logical Fallacies

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Theresa Devega

on 12 October 2015

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Transcript of Logical Fallacies

Draws an extreme conclusion from a premise.


If you watch Battlestar Galactica on Netflix, you'll get addicted to the show and want to stay home. You'll be so addicted to watching the show that you won't go to work and you'll lose your job and home.

The conclusion is false because this premise cannot be proven. It's highly possible to watch and enjoy Battlestar Galactica without losing everything in the process.
Straw Man Fallacy
The misrepresentation of a counterargument or an opponent’s position on your claim.

Ex: Members of the NRA who oppose gun control laws have no concern for those killed or injured from gun violence.

NRA members may be against gun control laws, but this in now way draw the logical conclusion that NRA members have no concern for victims, injured or killed as a result of guns.
Ad Hominen

Ad Hominem – A personal attack on one's opponent rather than their argument.

Ex: Kevin Harrison claims that the president has wavered on his job of successfully running the country in this second term. Harrison never took a Political Science course and rarely votes, so his opinion concerning the president has no merit.

Slippery Slope
Begging the Question

Circular argument/begging the question- occurs when an argument is restated rather than supported. This occurs when the premise and conclusion are joined in one statement.
Ex: "Women have a right to choose whether to have an abortion or not, therefore abortion should be allowed."

One of the best ways to make an inductive argument strong is by introducing a rebuttal to your claim and then overcoming the rebuttal appropriately. (In truth, you should do this for any persuasive writing you do.) It is best to observe the strongest counterargument to your claim, and treating fairly, overcome it.

In order to make the claim in inductive argument as accurate as possible, authors will use evidence through expert testimony, examples of real events, statistics, samples sizes, experiments etc.
Logical Fallacies of Presumption
Toulmin Method

Fallacies of Ambiguity
(The rhetorical triangle)
We have established that
is how the author represents their credibility in an argument.
is how the author appeals to their targeted audience. Some call pathos the emotional appeal.
We are now going to observe the role of
in your argument.

refers to the logic and reason found in your argument. Logos also refers to the organization, structure and content of your argument.

A syllogism is the third statement
that occurs after two

. T
he role of the syllogism is to evaluate reasons that form its conclusion.


All men are mortal.
(Premise #1 )

Socrates is a man.

(Premise #2)

Therefore, Socrates is mortal

This is a classic example of a syllogism
The conclusion is drawn from the 2 premises using
deductive reasoning.
If you agree with the premises, then you cannot deny the conclusion.
"lead down from"
Deductive arguments provide premises that lead to a conclusion, or logically point to your argument as being true.

A premise is a statement used to prove the conclusion; it is the stated assumption that something is true. Consider this the support to an argument (claim).

An argument is sound when the conclusion is proved by its true premises. A sound argument evaluates if the syllogism is valid and if the premises are true.
You can test if an argument is sound by observing and answering the following:
1. Are the premises true?
2. Is the argument a valid one?
For an argument to be valid, the conclusion must follow the premises. If you know the premises to be true, then you must accept the conclusion as true.

Example #1
All men are mortal. (Premise #1 ) True
Socrates is a man. (Premise #2) True
Therefore, Socrates is mortal. (Conclusion) Valid
This is a sound argument.

Example #2
The whale is a large fish. (Premise #1) Untrue
All large fish have scales. (Premise #2) Untrue
Therefore, whales have scales. False
In terms of the validity, this argument is valid. Even if the premises are false, we see how the conclusion is logically drawn from the premises. However,this is not a sound argument. For this to be a sound argument, the premises would need to be true and the argument valid.
Sound Arguments
Invalid Syllogisms
Let's look at an invalid syllogism.

All snakes are cold-blooded.
All snails are cold-blooded.
Therefore, all snails are snakes.

1. Rather than observe the validity of each premise, let's look at the conclusion.

2. Each premise may be true, but they in no way (logically speaking) lead to the conclusion. Snakes and snails may both be cold-blooded, but a shared trait does not necessarily mean that they are one and the same.
This is also an example of an unsound argument.
Induction is different from deduction. Deduction draws a conclusion (claim) based on true premises (evidence), while induction provides support to make a conclusion probable, but the conclusion (claim) is not always accurate.
Fallacies Relevance
Red Herring
Red herring- a way to distract from the actual argument or idea, rather than addressing it.

Ex: "The level of mercury in seafood may be unsafe, but what will fishers do to support their families?" (Purdue Owl)
Why study syllogisms?
Syllogisms make us better understand the strength of one's argument by evaluating its validity and whether or not it is sound.

Many argument are not limited to the structure of a syllogism, but this is an easy format by which we can learn about deductive reasoning and apply what we have learned to more complicated arguments.
Your claim is your argument, what you're working to establish as true.
This is the idea that you work to persuade readers of through deductive/inductive logic.

*While there are different types of persuasive texts and arguments, they all have a claim.

The grounds are the support for your claim.
Grounds are the provided reasons that point to your claim being true, or that serve to persuade one to believe or agree with your claim.

The warrant is the bridge that connects your grounds (support and evidence) to your claim.
Not all grounds need to be further explained regarding how they support the claim. Often times evidence that is explained works as the warrant.

Reasons to support the warrant are referred to as backing. The backing in an argument is the explanation to the audience for why the warrant proves how the grounds support the claim.

Texting while driving is dangerous and should be made illegal, in order to prevent injury and death.
Texting redirects a driver's focus from driving, distracting them from driving safely. According to the CDC, in 2011, 1 in 5 car accidents was due to driver distraction. And in 2012 driver distraction was the cause of 18 percent of all fatal crashes – with 3,328 people killed – and crashes resulting in an injury – with 421,000 people wounded" (FCC.gov). Furthermore,the Virginia Tech Transportation Institute concluded that texting while driving increases the risk of crashing 23 times more than driving without driver distractions ( FCC.org).
While statistics may not categorize the types of distractions that specifically caused each car accident and fatality, the evidence does point to how dangerous distractions are for drivers, and texting while driving is a major one.
A distraction, according to the National Highway Traffic Safety Administration, is one that may take a driver's eyes from the road, takes away the driver's cogntive focus on driving, and in some instances, may encourage the driver to remove their hand from the steering wheel while driving. Texting while driving falls into all three of these major driving distractions, as hands are required to send a text, eyes are needed to read, send and correctly type the text, and thought is required to read, understand and consider a response to the text. It is highly probable (
) that texting and driving was a big factor in the car crashes previously discussed, as texting is a major distraction to drivers.
Some drivers may agree that texting while driving is dangerous, but argue that making the act illegal will not prevent car accidents.
Or, There are times when an emergency occurs, and a driver must read and respond to a text.

Modal Qualifiers

Terms used to communicate the author's certainty regarding the claim. In other words, the words that express the strength between the claim and its grounds.
Hasty Generalization
A hasty generalization occurs when a conclusion is drawn from unrepresentative or insufficient evidence. Typically, a small sample is used to draw a more general conclusion or inaccurately represent a larger sample. A stereotype is also a form of this fallacy.

Ex: My neighbor is from Australia.
My neighbor drinks a lot of beer.
All Australians drink lots of beer.

False Analogy
Analogies are used to strengthen an argument, but when the ideas being compared, share a commonality, as well as being dissimilar, the analogy is false. If the difference between two ideas contrast with their similarities, you have a false analogy.

Example: If we can get man to walk on the moon, then we should be able to cure cancer.
Post Hoc Fallacy
The fallacy assumes that because something was caused after something else occurred, there is a causal relationship between the two. Just because B happened after A occurred, does not mean that B happened because of A.

Ex: Since Governor Brown took office, unemployment has dropped by 6 percent. Gov. Brown should be praised for reducing unemployment in California.
Tu Quoque
This fallacy occurs when one criticizes another, rather than address the argument. Rather than the address the argument, the person committing this fallacy will criticize their opponent, turning the focus away from them and the argument. (Appeal to hypocrisy.)

Ex: How can you urge me to stop drinking a bottle of wine a night when you drink wine all of the time?

Ex: You can't break your desk just because you wish to stretch your legs.
Sean broke his desk yesterday so he could have more leg room, so it's okay if I break my desk for more leg room.

Appeal to Authority
This fallacy occurs when one states something is true because a person judged to be an authority claims it is true.

Ex: Peter Singer says that eating meat is bad for our health, so eating meat must cause health problems if consumed.
Appeal to Ignorance
This fallacy occurs when one argues that the something is true, when in fact, the validity of a premise is unknown. The conclusion is drawn from a lack of evidence and it is inferred that the premise is true.
A is true because you cannot prove that A is false,
or B is false because you cannot prove B is true.

Ex: Since no one has been able to disprove the Loch Ness monster's existence, we can conclude that Nessie is real.

The Genetic Fallacy
This fallacy occurs when an argument or idea is discounted or accepted simply due to the source, or the origins, from where the idea or argument came.
Bob says to always keep an umbrella in your car if you live in Seattle, but Bob is a convicted felon, so his advice is not to be trusted.
This fallacy occurs when one misleads another using language (phrases) that have multiple meanings, misrepresenting the truth.

Ex: "Foreigners are hunting dogs."

Non Sequiter
This fallacy occurs when the conclusion is not logically deduced from its premises.

Ex: Kevin never eats onions and always requests "no onions" at restaurants. Kevin must be allergic to onions.
Ex: (1)The church would like to encourage theism.
(2)Theism is a medical condition resulting from the excessive consumption of tea.
(3) The church ought to distribute tea more freely.
This fallacy occurs when words or phrases are used in more than one way within the same argument. For the argument to not contain this fallacy, meaning of the word must remain the same throughout the argument.
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