A fallacy is a mistake in reasoning that can still be persuasive. Learning to name them makes them much easier to spot, in others and in yourself.

• Ad hominem: attacking the person instead of the argument. "You can't trust her view on taxes; she's divorced."
• Straw man: replacing someone's view with a weaker version, then knocking that down. "You want better police training? So you want no police at all."
• False dilemma: presenting two options as the only ones when others exist. "You're either with us or against us."
• Slippery slope: claiming one step will inevitably lead to an extreme outcome, without showing the chain. "Allow this and soon there will be total chaos."
• Appeal to popularity: "Millions believe it, so it must be true."
• Appeal to authority (misused): citing someone who isn't an expert on the topic, or treating any expert's word as final proof. A relevant expert consensus is good evidence; a celebrity endorsement is not.
• Begging the question (circular reasoning): the conclusion is hidden in a premise. "This book is reliable because the book says it is reliable."
• Equivocation: one word shifts meaning mid-argument. "Feathers are light. What is light cannot be dark. So feathers cannot be dark."

A word of caution

Spotting a fallacy shows that an argument fails. It doesn't show the conclusion is false. Treating it that way is itself a mistake, sometimes called the fallacy fallacy. A bad argument for a true claim is still possible.