Recognizing Common Informal Fallacies

1. Formal vs. Informal Fallacies

Before we dive into specific examples, it's useful to draw a distinction that will likely resonate with your background in physics and mathematics: the difference between formal and informal fallacies.

• Formal Fallacies are errors in the structure or form of a deductive argument. The argument is invalid regardless of the content of its premises. You can think of this as a "syntactic" error in reasoning. An example is affirming the consequent:

  1. If it is raining ($P$), then the ground is wet ($Q$).
  2. The ground is wet ($Q$).
  3. Therefore, it is raining ($P$).
     The structure If P then Q. Q. Therefore, P. is always invalid, no matter what $P$ and $Q$ represent.

• Informal Fallacies, which are our focus today, are errors in the content, context, or premises of an argument. The argument's structure might be formally valid, but the reasoning is still flawed. These are more like "semantic" or "pragmatic" errors.

The following short video provides a clear explanation of this distinction.

To help organize our exploration, we can group informal fallacies into broad categories. The following diagram gives one common way of classifying them. We will look at examples from each of the major branches.

2. Fallacies of Relevance

These fallacies occur when the premises of an argument are not logically relevant to the conclusion, even though they may seem psychologically relevant.

Straw Man

We begin with the fallacy that is the direct opposite of the Principle of Charity. A straw man argument occurs when you misrepresent, simplify, or distort someone's position to make it easier to attack.

Ad Hominem (Argument Against the Person)

This fallacy involves attacking the character, circumstances, or motives of the person making an argument instead of engaging with the substance of the argument itself.

The Stanford Encyclopedia of Philosophy (SEP) entry on fallacies, which is a great reference text, outlines three common variants of ad hominem:

• Abusive: Direct attack on the person's character.
• Circumstantial: Citing the person's circumstances (e.g., their job) as a reason to dismiss their claims.
• Tu Quoque ("you too"): Dismissing a person's advice or argument because they don't follow it themselves.

Appeal to Emotion (Argumentum ad Misericordiam)

This fallacy occurs when an arguer attempts to support a conclusion by evoking an emotional response (like pity or fear) in the listener, rather than by providing relevant evidence.

3. Fallacies of Ambiguity

This category includes fallacies that arise from the use of ambiguous or imprecise language.

Equivocation

This fallacy exploits the ambiguity of a word or phrase that has different meanings in different parts of the argument. This shift in meaning breaks the chain of reasoning.

The Berkeley resource on fallacies frames this in a way you might find useful. An equivocation often hides a formal fallacy. For the example All men should have the right to vote. Sally is not a man. Therefore, Sally should not have the right to vote, the error is concealed by the word "man" meaning "human" in one premise and "male" in the other. If we disambiguate the terms, the invalid structure becomes obvious.

4. Fallacies of Presumption

These fallacies involve arguments that depend on a dubious or unstated assumption.

Begging the Question (Petitio Principii)

This is one of the most misunderstood fallacies. It does not mean "to raise the question." Begging the question is a fallacy of presumption where an argument's premises assume the truth of the conclusion, instead of providing independent support for it. This is also known as circular reasoning.

For example, the argument "Free speech is important for the state because it is vital for the community that everyone can express their sentiments without restriction" begs the question. The premise is just a rephrasing of the conclusion.

Slippery Slope

This fallacy occurs when an arguer claims that a certain action will inevitably lead to a chain of undesirable events, without providing sufficient evidence that the chain reaction will actually occur.

5. A Quick Review

The following infographic provides a fun and memorable summary of some of the fallacies we've discussed, along with a few others. See if you can identify the error in each robot's argument.

Your Turn: Identify the Fallacy

Let's test your ability to spot these errors. For each argument below, identify the primary informal fallacy being committed.

1. "Dr. Evans argues that the new particle accelerator is perfectly safe. But what do you expect from someone whose research funding depends entirely on the project going forward? We can't trust his safety analysis."
2. "We must have a law against cloning. If we allow human cloning, it's only a matter of time before we have genetically engineered subspecies, designer babies for the rich, and a complete breakdown of the family unit. It will be the end of society as we know it."
3. "The teachings of this spiritual guru are clearly true, because he is an enlightened master. We know he is an enlightened master because he says so, and an enlightened master would never lie."
4. "My opponent says we should increase funding for public transportation. I can't believe he wants to take away everyone's cars and force us all onto crowded, inefficient buses. This is an attack on our freedom and personal mobility."

. . .

Answers

1. Ad Hominem (Circumstantial): The argument attacks Dr. Evans's circumstances (his funding source) as a reason to reject his analysis, rather than addressing the analysis itself.
2. Slippery Slope: It posits a dramatic chain of negative consequences from a single action (allowing cloning) without sufficient evidence that these consequences are inevitable.
3. Begging the Question (Circular Reasoning): The argument is circular. The truth of the teachings depends on the guru being enlightened, and the evidence for his enlightenment is his own claim, which is assumed to be true because he is enlightened.
4. Straw Man: The opponent's position (increase funding for public transport) is distorted into a much more extreme and unpalatable position (take away all cars) that is easy to attack.

Conclusion

Today we have surveyed the landscape of informal fallacies, learning to identify several common patterns of flawed reasoning. Recognizing these errors is a foundational skill in philosophy, allowing you to critically evaluate arguments and avoid making similar mistakes yourself.

Key Takeaways:

• Informal fallacies are errors in reasoning related to an argument's content, context, or premises, as opposed to formal fallacies, which are errors in its logical structure.
• Fallacies of Relevance like the Straw Man, Ad Hominem, and Appeal to Emotion introduce information that is not logically relevant to the conclusion. Many of these are violations of the Principle of Charity.
• Fallacies of Ambiguity, such as Equivocation, arise from the imprecise use of language, where a term's meaning shifts during an argument.
• Fallacies of Presumption, like Begging the Question and the Slippery Slope, rely on unproven or unwarranted assumptions to reach their conclusions.

Preview of the Next Lesson:

In this lesson, we made an important distinction between formal (structural) and informal (content-based) fallacies. In our next and final lesson of this introductory module, we will explore this distinction more deeply by examining the difference between an argument's formal structure (syntax) and its truth-based content (semantics). This will provide the final piece of conceptual groundwork before we transition into the rigorous world of propositional and predicate logic in Module 2.