Overview

Logical fallacies are errors in reasoning that undermine the logic of an argument. They can be either formal (errors in logical structure) or informal (errors in content or context).

Why Study Fallacies?

  • Improve critical thinking skills
  • Evaluate arguments more effectively
  • Avoid making these errors yourself
  • Recognize manipulation and poor reasoning

Important Note

Identifying a fallacy doesn't automatically make an argument's conclusion false. It simply means the reasoning provided doesn't adequately support the conclusion.

Formal Fallacies

Formal fallacies are errors in the logical structure of an argument, making the argument invalid regardless of the truth of its premises.

Affirming the Consequent

Structure:
If P, then Q
Q
Therefore, P

Example:
If it's raining, then the ground is wet
The ground is wet
Therefore, it's raining

Denying the Antecedent

Structure:
If P, then Q
Not P
Therefore, not Q

Example:
If it's raining, then the ground is wet
It's not raining
Therefore, the ground is not wet

Why These Are Fallacies

These commit the error of confusing sufficient conditions with necessary conditions. Just because rain causes wet ground doesn't mean rain is the only cause of wet ground.

Informal Fallacies

Informal fallacies are errors in reasoning that occur due to problems with content, context, or the way language is used.

Categories of Informal Fallacies

  • Fallacies of Relevance: Irrelevant premises
  • Fallacies of Weak Induction: Insufficient evidence
  • Fallacies of Presumption: Unwarranted assumptions
  • Fallacies of Ambiguity: Unclear language

Context Matters

Unlike formal fallacies, whether an informal fallacy has been committed often depends on the specific context and content of the argument.

Ad Hominem

Ad hominem fallacies attack the person making an argument rather than addressing the argument itself.

Types of Ad Hominem

Abusive Ad Hominem

Example:
"You can't trust John's argument about climate change because he's an idiot."

Circumstantial Ad Hominem

Example:
"Of course the tobacco company CEO says smoking isn't harmful—he profits from cigarette sales!"

Tu Quoque (You Too)

Example:
"You say I shouldn't speed, but you speed too!"

When Personal Factors Matter

While ad hominem attacks are generally fallacious, there are cases where a person's character or circumstances are relevant to evaluating their testimony or credibility.

Straw Man

The straw man fallacy involves misrepresenting someone's argument to make it easier to attack.

How It Works

  1. Person A makes argument X
  2. Person B restates Person A's argument as weaker argument Y
  3. Person B attacks argument Y
  4. Person B concludes that Person A's position is wrong
Example:
Person A: "We should have stricter gun control laws."
Person B: "Person A wants to take away all our guns and leave us defenseless. This is clearly wrong because people have a right to self-defense."

Avoiding Straw Man

  • Carefully restate your opponent's position
  • Ask for clarification if unsure
  • Address the strongest version of their argument
  • Use direct quotes when possible

Steel Man Alternative

Instead of straw manning, consider "steel manning"—presenting the strongest possible version of your opponent's argument before addressing it.

False Dilemma

Also known as false dichotomy or either/or fallacy, this presents only two options when more exist.

Examples:
"You're either with us or against us."

"Either we ban all cars or we'll destroy the environment."

"You either believe in God or you're immoral."

Why It's Problematic

  • Oversimplifies complex issues
  • Ignores middle ground positions
  • Forces premature decision-making
  • Can be used to manipulate choices

When Dichotomies Are Valid

Sometimes there really are only two options (e.g., "Either the light is on or it's off"). The fallacy occurs when additional options exist but are ignored.

Slippery Slope

This fallacy assumes that one event will inevitably lead to a chain of negative consequences without adequate evidence.

Example:
"If we allow students to redo one test, soon they'll expect to redo all tests, then all assignments, and eventually school will become meaningless."

Elements of Slippery Slope

  1. Initial action or event
  2. Chain of consequences
  3. Undesirable final outcome
  4. Lack of evidence for the chain

Legitimate Slippery Slope Arguments

Not all slippery slope arguments are fallacious. They're valid when:

  • Each step in the chain is likely
  • There's evidence for the progression
  • There are no effective stopping points

Evaluating Slippery Slopes

Ask: Is there good reason to believe each step will lead to the next? Are there natural stopping points? What evidence supports the claimed progression?

Avoiding Fallacies

Understanding logical fallacies is essential for clear thinking and effective argumentation.

Strategies for Better Reasoning

  • Study logic: Understand valid argument forms
  • Slow down: Take time to analyze arguments carefully
  • Question assumptions: Examine unstated premises
  • Seek evidence: Look for support beyond mere assertion
  • Consider alternatives: Are there other explanations?

Common Fallacies in Religious/Philosophical Debates

  • Appeal to authority: "This must be true because an expert said it"
  • Appeal to ignorance: "We can't prove God doesn't exist, so God exists"
  • Begging the question: "The Bible is true because God wrote it, and God exists because the Bible says so"
  • False analogy: "The universe is like a watch, so it must have a designer"

A Balanced Approach

While it's important to identify fallacies, be careful not to become overly focused on fallacy-hunting at the expense of genuine engagement with arguments. The goal is better reasoning, not winning debates through technicalities.

Final Thoughts

Logical fallacies are tools for improving reasoning, not weapons for destroying opponents. Use your knowledge of fallacies to strengthen your own arguments and to engage more thoughtfully with others' ideas, always maintaining intellectual humility and openness to correction.