8.1 Formal vs. Informal Fallacies

Fallacies can trip up even the sharpest thinkers. They come in two main flavors: formal ones that mess up the argument's structure, and informal ones that use sneaky content. Knowing the difference helps you spot weak reasoning.

Informal fallacies are trickier beasts. They can distract you, play with your emotions, or oversimplify things. Watch out for attacks on character, appeals to irrelevant authorities, false either/or choices, and slippery slope arguments in everyday life.

Types of Fallacies

Formal vs informal fallacies

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• Formal fallacies occur when the structure of the argument is invalid, meaning the conclusion does not follow logically from the premises (affirming the consequent, denying the antecedent)
• Informal fallacies occur when the content of the argument is flawed or misleading due to irrelevant, ambiguous, or unsupported premises or reasoning based on false assumptions or emotional appeals

Characteristics of informal fallacies

• Fallacies of relevance involve premises that are not relevant to the conclusion (ad hominem, appeal to authority, red herring)
• Fallacies of ambiguity use unclear or misleading language in the argument (equivocation, amphiboly, accent)
• Fallacies of presumption rely on false or unsupported assumptions (begging the question, false dilemma, slippery slope)

Impact and Examples of Informal Fallacies

Impact on argument validity

• Distract from the main issue by introducing irrelevant information, leading the audience away from the central point
• Manipulate emotions like fear, pity, or anger to persuade the audience
• Oversimplify complex issues by presenting them as black-and-white, ignoring nuances and alternative perspectives
• Create the illusion of strong evidence, making arguments appear more convincing than they actually are

Examples in everyday reasoning

• Ad hominem attacks the character of the person making the argument instead of addressing the argument itself ("You can't trust his opinion on climate change; he's just a politician, not a scientist.")
• Appeal to authority claims an argument is true because an authority figure supports it, even if the authority's expertise is not relevant ("This new diet must be effective because a famous celebrity endorses it.")
• False dilemma presents a situation as having only two possible options when there are actually more alternatives ("Either we invest in this expensive project, or our company will go bankrupt.")
• Slippery slope argues that one event will inevitably lead to a chain of worse events without sufficient evidence ("If we allow same-sex marriage, it will lead to people marrying their pets.")