What a fallacy is
An argument offers reasons for a conclusion. A logical fallacy is a pattern of reasoning in which the reasons do not actually support the conclusion, even though they may seem to. The conclusion could still be true; a fallacy only tells you that this particular argument has not shown it.
That distinction matters. Spotting a fallacy is a reason to ask for better support, not a way to declare the other person wrong. It is also easy to misuse. Pointing out a “fallacy” in every disagreement can become its own way of avoiding the substance, so it is best used as a tool for your own thinking first.
The examples below are deliberately mundane.
Ad hominem
An ad hominem argument attacks the person instead of the claim. “You can’t trust her recommendation for a study schedule; she failed a test once.” Whether the schedule is a good one depends on how it works, not on the speaker’s record.
There is a nuance. A person’s interests can be relevant when judging a claim, for example if a seller praises their own product. That is a reason to look for independent confirmation, not a reason to dismiss the claim outright.
Straw man
A straw man misrepresents someone’s position in a weaker form and then attacks that version. If one person says “we should spend a little less time on homework,” and the reply is “so you think students should never learn anything,” the reply has swapped the original view for an exaggerated one.
A useful check is to restate the other side’s argument in a way they would accept before you respond to it.
False dilemma
A false dilemma presents two options as if they were the only ones. “Either you study every night or you will fail the course.” In reality there are usually other possibilities, such as studying on some nights, using shorter sessions, or getting help with the hard parts. When you see “either… or,” ask what has been left out.
Appeal to authority
Citing an expert can be perfectly reasonable when the person has relevant expertise and their view reflects wider agreement in the field. It becomes a fallacy when the authority is speaking outside their area, when the “expert” is unnamed, or when the authority replaces any actual evidence. “A famous chef says this vitamin prevents illness” is a weak argument because cooking expertise does not extend to medicine.
Appeal to popularity
“Everyone is doing it” or “millions of people believe it” treats the number of supporters as proof. Popular ideas have turned out to be wrong many times. Popularity may be a clue worth investigating, but it is not evidence of truth.
Slippery slope
A slippery slope argument claims that one small step will inevitably lead to a chain of extreme results, without showing why each link would follow. “If we allow open-book tests, soon nobody will learn anything.” Some chains of events are real, so the question to ask is whether each step is actually supported.
Circular reasoning
Circular reasoning assumes what it is trying to prove. “This guide is reliable because it says it is reliable.” The conclusion is hiding in the premise. These can be hard to see in longer passages, where the loop is spread across several sentences.
Hasty generalization
A hasty generalization draws a broad conclusion from too few or unrepresentative examples. “I asked three friends and they all liked the new app, so everyone will.” A sample of three people you know tells you little about a large population. This links to the question of sample size and selection discussed in basic probability, where small samples can mislead.
Post hoc reasoning
The Latin phrase post hoc means “after this.” The fallacy assumes that because one event followed another, the first caused the second. “I wore my blue shirt and then passed the exam.” Sequence is not cause. The related problem of things that merely occur together is explored in more depth in the idea of correlation causation, which separates patterns from causes.
Cherry-picking and the red herring
Cherry-picking presents only the evidence that supports a point and leaves out the rest. A red herring changes the subject to something that sounds relevant but is not. If a question about the cost of a course is answered with a story about how friendly the teachers are, the original question has been sidestepped.
Appeal to nature and appeal to emotion
“It is natural, so it must be good” and “it is artificial, so it must be bad” are both weak, since plenty of natural things are harmful and plenty of manufactured things are helpful. Appeals to emotion try to win agreement through fear, pity or anger rather than reasons. Emotion is not out of place in an argument, but it should not stand in for evidence. This is one of the patterns often seen in misinformation spotting.
Responding well
- Ask a question first: “What makes you think that follows?”
- Name the gap politely rather than the label. Saying “I’m not sure that one thing leads to the other” tends to go further than announcing a fallacy.
- Check your own reasoning with the same care.
- Remember that an argument can be flawed while its conclusion is true, and the reverse.
Knowing these patterns will not make you immune to them, and many real arguments mix several. Treat the list as a set of prompts for careful reading rather than a scoring system.