Unit 2.4 Understanding Fallacies in Reasoning

Fallacy

An error in reasoning that may nevertheless appear at first glance to be correct reasoning (Herrick 2010:199).

Formal fallacy

An error in reasoning that arises in virtue of the logical structural form of the argument alone (rather than the content).

e.g. Affirming the Consequent: If P then Q; Q, therefore P.

• Denying the Antecedent: If P then Q; Not P, therefore not Q.

Informal fallacy

An error in reasoning that arises in virtue of the content of the reasoning alone (rather than the logical form).

Affirming the Consequent

A formal fallacy where the argument takes the form: If p then q, q, therefore p.

Affirming the Antecedent

A valid argument form where the argument takes the form: If p then q, p, therefore q.

NEVER A FORMAL FALLACY since valid

• e.g. "If it rains (P), the ground is wet (Q). It rained (P). Therefore, the ground is wet (Q)."

Denying the Antecedent

A formal fallacy where the argument takes the form: If p then q, not p, therefore not q.

e.g. "If it rains (P), the ground is wet (Q). It did not rain (Not P). Therefore, the ground is not wet (Not Q)." (Invalid, as the ground could be wet from sprinklers)

Denying the Consequent

A valid argument form where the argument takes the form: If p then q, not q, therefore not p.

Ad Hominem Fallacy

Rejecting a claim or argument by attacking the person who makes it rather than rationally assessing the claim/argument itself.

Argument A

1. All cats are 4-legged creatures; 2. All dogs are 4-legged creatures; Therefore, 3. All dogs are cats.

Argument B

1. All planets are spherical objects; 2. All tennis balls are spherical objects; Therefore, 3. All tennis balls are planets.

Argument C

1. All As are Bs; 2. All Cs are Bs; Therefore, 3. All Cs are As.

Example of Formal Fallacy

1. If Bill Gates earns a huge amount of money, then he's rich; 2. Bill Gates is rich; Therefore, 3. Bill Gates earns a huge amount of money.

Example of Valid Reasoning

1. If Oprah Winfrey earns a huge amount of money, then she's rich; 2. It's not the case that Oprah Winfrey earns a huge amount of money; Therefore, 3. It's not the case that she is rich.

Example of Non-Fallacious Argument

1. If Oprah Winfrey earns a huge amount of money, then she's rich; 2. It's not the case that Oprah Winfrey is rich; Therefore, 3. It's not the case that she earns a huge amount of money.

Example of Informal Fallacy

1. If Mia is a Liberal, Mia can't be trusted; 2. Mia is a Liberal; Therefore, 3. Mia can't be trusted [for anything].

Example of Hypocritical Argument

1. We may reasonably ignore all arguments made by 'hypocrites'; 2. X is hypocritical; Therefore, we may ignore X's arguments.

Tu quoque fallacy

Discrediting an argument due to hypocrisy. “You too”. Discrediting a person’s argument merely because they don’t act/live consistently with its conclusion.

Genetic fallacy

Fallacy that occurs when a claim is accepted or rejected based solely on its source or origin, rather than its content.

“People only believe that there is a God because they need an “invisible parent figure” that will help them cope with an “irrational and hostile world”. So, we should reject their claims about God and become atheists.” The Fallacy: Assuming that because a belief provides comfort or stems from a psychological need, it cannot also be true.

Composition fallacy

Assuming what's true of parts is true for the whole.

e.g. If an individual stands up at a football game, they can see better. Therefore, if everyone stands up, everyone can see better". (In reality, the view remains obstructed).

e.g. I can afford product 1. I can afford product 2. ….. Therefore, I can afford all products combined. The sum of the parts (total cost) likely exceeds the budget, even if individual parts do not.

Division fallacy

Assuming what's true of the whole is true for parts.

e.g. The US government is highly inefficient. Therefore, this specific House Speaker must be inefficient.

Appeal to popularity

Claiming something is true because many believe it.

BANDWAGON

When someone argues that a belief, action, or product is correct, true, or good simply because a large number of people believe, do, or use it.

e.g.

"Everyone is voting for this candidate, so they must be the best choice."

False dilemma

Presenting only two choices when more exist.

Appeal to ignorance

A logical fallacy claiming a proposition is true simply because it hasn't been proven false, or false because it hasn't been proven true.

e.g. No one has ever successfully proved that God exists, therefore God does not exist," or conversely, "No one has ever proved that God does not exist, therefore He does,".

Appeal to emotion

Using emotions as premises in an argument.

"Officer, I know I was speeding, but I’ve had a terrible week and my life is falling apart. Can't you let me off?". The driver uses pity to deflect from the evidence of speeding.

Red herring

Introducing irrelevant issues to distract from the argument.

e.g. "I know I forgot to wash the dishes, but look how clean the living room is!" (Diverts from chores to cleanliness). Think of toxic boyfriends

Straw man fallacy

Distorting, exaggerating, or misrepresenting an opponent's argument to make it easier to attack an opponent's position for easier attack.

e.g. We should tighten regulations on emissions to help the environment."

• Person B: "So you want to destroy the economy and put thousands of people out of work?"

Begging the question

A logical fallacy where the premise of an argument assumes the truth of its conclusion, often resulting in circular reasoning.

e.g. Freedom of speech is important because people should be able to speak freely.

e.g. Ghosts are real because I have experienced things that can only be explained by paranormal activity.

Slippery slope

Arguing one step leads to extreme consequences.

e.g. If we allow this small tax increase, the government will eventually take 100% of our income

Hasty generalization

Drawing conclusions from insufficient evidence.

e.g. steoreotyping. I met two people in London and they were both rude. Therefore, everyone in London is rude.

e.g. medical claims: My grandfather smoked a pack a day and lived to be 95, so smoking isn't actually bad for you

Relativity effect

Decisions influenced by comparative options.