Week 7 · Chapter

Chapter 7 — Fallacies of Relevance

Critical Thinking Free sample edition

The module's primary reading · ~35–45 minutes · Objective 4 (with Objective 2 carried forward) · Read it first this week; the lecture, the slides, the tutorial, the quiz, and the Argument Workshop all build on it.

In plain language

This week is about reasons that miss the point. You will learn what a fallacy is (a flaw in the reasoning, not in the facts) and run one question on every reason you hear: if this were true, would it bear on the conclusion? You will meet nine common ways a reason can miss, including the attack on the person (going after the speaker instead of the reasons), the straw man (answering a weaker view nobody stated), and the red herring (changing the subject). You will also learn when an expert's word is good evidence and when it is not. These tests help you set aside what is loud in an argument and weigh what is relevant.

Why you already care about this

A student club posts its spring budget in the group chat. The treasurer has listed 4 costs, 2 sources of money, and a total. Within a minute, a member replies: "We can ignore the treasurer's budget proposal; she failed a math class in high school." Three people react with a laughing face. Nobody checks the total.

You have seen replies like that. A roommate brushes off your advice because you once did the same thing. An ad tells you that your family will be the next victims if you don't buy today. A famous face on a screen says a product works. In each case, something is offered as a reason, and it feels like one. The question this week is whether it bears on the conclusion at all.

For six weeks you tested arguments by their shape and by their words. This week you test their relevance: whether the premises, even if true, connect to the conclusion they are meant to support.

By the end of this chapter you will be able to:

tell a fallacy, a flaw in reasoning, from a false premise, a flaw in content;
run the relevance test on a premise and say in words whether it bears on the conclusion;
identify the attack on the person, the you-too, and the circumstantial attack, and say when a conflict of interest is a relevant point about testimony instead;
identify a straw man and map the real objection it replaces as an arrow marked "against";
identify appeals to fear, pity, and popularity, and the red herring, while recognizing emotion that fits good reasons;
tell an appeal to unqualified authority from relevant, agreed expertise, and name Locke (1690) as the classic source of the Latin names.

Carry this line with you: a true reason can still be the wrong reason — ask whether it bears.

Where we are

Already covered: Week 1 taught you to find an argument. Week 2 taught you standard form, the supplied premise, and argument maps with objections marked "against". Week 3 taught you validity, soundness, strength, and the counterexample method. Weeks 4 and 5 taught you the deductive forms. Week 6 taught you how words can shift meaning or carry a verdict.
This week: a fallacy set apart from a false premise, then the fallacies of relevance: three attacks on the person, the straw man, the appeals to fear, pity, and popularity, the red herring, and the unqualified authority. Locke (1690) supplies the Latin names.
How they connect: Week 2's map shows where an objection should land, and this week shows what happens when it lands somewhere else. Week 3's line between validity and truth becomes the line between a fallacy and a false premise.
Where we're going next: Week 8 closes the first half of the course with a cumulative review, a short look at the fallacies of presumption (arguments that quietly assume what they should support), and the midterm.

Week 1 gave you the habit of finding the conclusion and the reasons offered for it. Week 2 gave you standard form, with the running question written as P1, P2, P3 (supplied), P4, and C, and a map in which an objection is an arrow marked "against". Week 3 showed that an argument can be valid with a false premise. Week 6 showed that a word can carry a verdict without arguing for it. This week asks a plainer question of each premise: does it bear on the conclusion?

1. Test the link: fallacy versus false premise

Picture two friends arguing about a café. One says, "The café on the corner is closed for repairs this week, so we can't go there tomorrow." If the café is in fact open, that argument fails, but its reasoning is fine. The trouble is in the facts. Now picture the other friend: "Everyone I follow online loves that café, so its food must be good." Even if that premise is true, it does not show the food is good. The trouble is in the reasoning.

Those two failures have different names.

A fallacy is a flaw in the reasoning that connects an argument's premises to its conclusion, so that the premises fail to support the conclusion even when they are true.

A false premise is a premise that is not true, a flaw in an argument's content rather than in its reasoning; an argument can have a false premise and still be valid.

This week's fallacies share a family name. A fallacy of relevance is a fallacy whose premises, even if true, do not bear on whether the conclusion is true, such as an insult, a feeling, or a head count offered in place of reasons.

The test that finds them is one question, the relevance test: if this premise were true, would it bear on whether the conclusion is true? If it would not, the premise is beside the point, however true or moving it is.

The study of fallacies is old. It begins with Aristotle's Sophistical Refutations, a work the course names without a date. The names you will learn this week are a modern catalog, a classroom tool for organizing judgment. No catalog settles a real case by itself; it gives you the questions to ask.

Worked example — the two café arguments (illustrative). Sort each failure.

"The café is closed for repairs this week, so we can't go tomorrow." Run the relevance test. If the café really were closed all week, that would bear directly on whether you can go tomorrow. The reasoning connects. If the premise is false, the argument has a false premise, not a fallacy.
"Everyone I follow loves that café, so its food must be good." Run the relevance test. Even if every account you follow loves it, popularity does not settle whether the food is good. The reasoning does not connect, so the argument commits a fallacy, whatever the facts turn out to be.

In words: the first argument can fail only because a premise is false, and the second fails even with a true premise, because its premise does not bear on its conclusion.

Misconception check — a false premise is a fallacy. Students often call any argument with a false claim in it "a fallacy." That is tempting, because in everyday speech "fallacy" means any mistaken belief. But in this course a fallacy is a flaw in the reasoning. An argument can be valid with a false premise, as Week 3 showed, and it can be fallacious with every premise true. Check the link first; check the facts separately.

Memory hook: a fallacy breaks the link; a false premise breaks the facts.

2. Answer the reasons, not the person: attacks on the person

Go back to the group chat. The reply about the treasurer's old math grade never looks at the budget. If the budget adds up, it adds up whoever wrote it. That is the most common fallacy of relevance, and it comes in three versions.

The attack on the person (ad hominem) is the fallacy of rejecting a claim or argument because of a fact about the person who made it rather than because of the reasons offered.

The you-too (tu quoque) is the version of the attack on the person that dismisses advice or criticism because the adviser does not follow it, as if inconsistency made the advice unsound.

The circumstantial attack on the person is the version of the attack on the person that dismisses a claim because of the arguer's situation or interests, such as what they sell or stand to gain, instead of checking the reasons.

Worked example — three attacks on the person (illustrative). Run the relevance test on each passage from the course's fallacy set.

The treasurer. "We can ignore the treasurer's budget proposal; she failed a math class in high school." A grade from years ago does not bear on whether this budget adds up, so the passage commits the attack on the person (ad hominem).
The doctor. "My doctor told me to cut back on soda, but she drinks soda herself, so I don't have to listen." Whether the adviser follows the advice does not bear on whether the advice is sound, so the passage commits the you-too (tu quoque).
The bike-shop owner. "Of course the bike-shop owner supports bike lanes downtown; he sells bikes, so his reasons don't count." His interest may be a reason to check his reasons, but it does not show they fail, so the passage commits the circumstantial attack on the person.

In words: each passage turns from the claim to the person who made it, and none of the facts about the person bears on whether the claim is true.

Now the non-fallacious neighbor. Some facts about a person do matter, but only to one question: how much to trust what they tell you. A conflict of interest is a situation in which a person stands to gain or lose from what others believe, such as a paid spokesperson; it is a reason to weigh their testimony with care, not a refutation.

Testimony is a report by a person that something is so, offered for others to rely on; its weight depends on the person's expertise, track record, and independence from the outcome.

Here is the contrast case the course discusses and never keys (illustrative). A spokesperson in an ad says a blender is the quietest on the market, and the blender's maker pays the spokesperson. Noting that payment is fair. It tells you to look for independent evidence before taking the spokesperson's word. It does not show the blender is loud. If the ad also gives test results, those results stand or fall on their own.

Misconception check — any criticism of a person is an attack on the person. Students often learn this fallacy and then flag every sentence that mentions the speaker. That is tempting, because the pattern looks the same on the surface. But pointing out a documented conflict of interest, or a record of getting things wrong, is relevant when the question is how far to trust someone's testimony. It becomes a fallacy only when it is offered as a refutation of the argument itself.

An honesty note: real conversations blur these lines. "He sells bikes, so let's check his traffic figures against the city's counts" is fair; "he sells bikes, so his reasons don't count" is the fallacy. The words around the fact decide which job it is doing, and a borderline case is for discussion, not a quiz.

Memory hook: weigh the testimony, answer the reasons.

3. Answer the real view: the straw man

A city proposes closing one downtown parking lot one morning a week for a farmers' market. A resident writes to the local paper: "So its supporters want to ban cars from downtown." The resident then argues, at length, that a car ban would hurt businesses. That argument might be a good one. It answers a proposal nobody made.

A straw man is the fallacy of answering a weaker or distorted version of the opposing position instead of the position actually stated, so the reply knocks down a view nobody holds.

You already have the cure from Week 2. The principle of charity says to choose, among the readings the words allow, the one that makes an argument as reasonable as possible. A straw man does the opposite: it picks the reading that is easiest to beat.

Worked example — the farmers' market and the running question (illustrative). Compare the position stated with the position answered.

The farmers' market. Stated: close one lot, one morning a week, for a market. Answered: ban cars from downtown. The reply answers a position nobody stated, so the passage commits the straw man.
The running question, in standard form. Here is the argument as Week 2 set it out.

P1: During finals week many students need a quiet, safe place to study late at night.

P2: The library is the only quiet, safe, well-lit study space on campus large enough to meet that need.

P3 (supplied): The campus should provide study space students need during finals when it can do so at modest cost.

P4: Keeping the library open overnight for the five nights of finals week costs about 1,600 dollars in staff wages.

So,

C: The campus library should stay open around the clock during finals week.

The real objection. Overnight hours encourage all-night studying, and losing sleep can hurt exam performance, so the library would be helping students harm themselves. On the map, this objection is a box with an arrow marked "against" pointing at C. It is a serious objection, and a reply has to meet it.
The straw man. "They want the library to be a dorm." No premise says students should live or sleep in the library. Knocking that claim down leaves P1, P2, P3 (supplied), P4, and C untouched, because it attacks a box that is not on the map.

In words: the market reply and the dorm reply each answer a position nobody stated, so each is a straw man, while the sleep objection answers the argument actually made and deserves a reply.

Misconception check — a straw man is a strong objection. Students often admire a straw-man reply because it sounds confident and wins easily. That is tempting, because the reply's own reasoning may be sound. But a reply is only as good as its aim. Before you judge any objection, write the original position in standard form and check that the objection's arrow points at a box that is really there.

Memory hook: map the real view before you answer it.

4. Weigh the feeling: appeals to fear, pity, and popularity

A home-security ad shows a dark window and a shadow. The voice-over says, "Install our home-security app today, or your family will be the next victims of a break-in." The ad never says how the app works or whether it lowers break-ins. It hands you a feeling and asks you to act on it.

Three fallacies of relevance work this way.

The appeal to fear is the fallacy of offering fear of a bad outcome in place of evidence that the conclusion is true, as when an ad warns of disaster instead of showing that its product works.

The appeal to pity (ad misericordiam) is the fallacy of offering sympathy for someone's situation or feelings in place of reasons that bear on whether the conclusion is true.

The appeal to popularity (ad populum) is the fallacy of offering the number of people who believe something in place of reasons that bear on whether it is true.

Worked example — the ad, the grade, and the group chat (illustrative). Run the relevance test on each passage from the fallacy set.

The security app. "Install our home-security app today, or your family will be the next victims of a break-in." Fear is offered in place of evidence that the app works, so the passage commits the appeal to fear.
The A grade. "I should get an A in this course; I worked really hard, and I'll be crushed if I don't." Disappointment does not bear on whether the work met the standard for an A, so the passage commits the appeal to pity (ad misericordiam).
The group chat. "Most people in the group chat think the new attendance rule is unfair, so it must be unfair." A head count is offered in place of reasons, so the passage commits the appeal to popularity (ad populum).

In words: each passage offers a feeling or a head count where a reason should be, and none of them tells you whether its conclusion is true.

Emotion is not the problem. Suppose a forecast shows a strong storm heading for the coast, and a family feels afraid and leaves early. Their fear fits the evidence, and the evidence carries the argument. Or suppose a friend's hard week makes you want to help with their move. Sympathy can be a fitting reason to act kindly. The fallacy is in letting a feeling stand in for reasons on a question the feeling cannot answer, such as whether an app works or whether an essay earned an A.

Misconception check — emotion in an argument is a fallacy. Students often flag any passage that makes them feel something. That is tempting, because the appeal to fear and the appeal to pity are named after feelings. But an argument can be moving and still be good when the emotion is a fitting response to good reasons. Ask what the feeling replaces. If it replaces the evidence, it is a fallacy; if it rides alongside the evidence, it is not.

An honesty note on popularity: what many people believe is sometimes a reasonable clue, for instance when the many are specialists who have checked the evidence. That is an appeal to experts, which section 6 covers. "Most people in the group chat think so" is a head count of opinions, and a head count does not settle whether a rule is unfair.

Memory hook: ask what the feeling replaces.

5. Stay on the question: the red herring

At a campus forum, a student asks the shuttle spokesperson a direct question: does the late-night shuttle run often enough? The spokesperson smiles and says the shuttles were recently repainted in the school colors. The room applauds the colors. The question about how often the shuttle runs is still sitting there.

A red herring is the fallacy of changing the subject to a different issue and treating the new issue as if it settled the original one.

A red herring differs from a straw man. A straw man answers a distorted version of the same issue. A red herring leaves the issue entirely and hopes nobody notices.

Worked example — the shuttle (illustrative). "Asked whether the late-night shuttle runs often enough, the spokesperson answers that the shuttles were recently repainted in the school colors."

State the original question. Does the late-night shuttle run often enough?
State the issue the answer raises. Do the shuttles look good?
Run the relevance test. If the shuttles were freshly painted, would that bear on how often they run? It would not.

In words: the new paint is a different issue from how often the shuttle runs, so the passage commits the red herring.

The cure is to write the original question down and hold it. When an answer arrives, check it against the question, not against how satisfying it sounds. A fair answer might be "every 20 minutes until 2 a.m." or "not often enough, and here is our plan." Either one is on the question.

Misconception check — any change of topic is a red herring. Students often call every turn in a conversation a red herring. That is tempting, because people change topics all the time. But a new topic is a fallacy only when it is offered as if it settled the original question. "Good question; first, the shuttles were repainted, and second, they run every 20 minutes" changes the subject and then comes back. Check whether the original question ever gets answered.

Memory hook: write the question down; hold the answer to it.

6. Check the expert: appeals to authority

You rely on experts every day. You take a pharmacist's word on a dosage and a mechanic's word on your brakes, and that is good reasoning. You cannot check everything yourself. The question is not whether to trust experts. It is which appeals to experts deserve your trust.

An appeal to authority is an argument that a claim is true because an authority says so; it is good inductive evidence when the authority has relevant expertise, experts broadly agree, and no serious conflict of interest exists.

An appeal to unqualified authority (ad verecundiam) is the fallacy of resting a claim on an authority when relevant expertise, expert agreement, or independence is missing, most often when the authority speaks outside their field.

That gives you three checks to run on any appeal to an expert:

Relevant expertise. Is this person an expert on this question, not only on some question?
Broad agreement. Do the experts in that field broadly agree, or are they divided?
No serious conflict of interest. Does the authority stand to gain from your believing it?

Worked example — the actor and the forecast (illustrative). Run the three checks on each.

The actor. "A famous actor says this herbal supplement cures colds, so it works." Check one fails at once: acting is not expertise in medicine. The passage commits the appeal to unqualified authority (ad verecundiam).
The forecast. A national weather service forecasts a storm's path, and a club cites that forecast as a reason to move its outdoor event. The forecasters are experts on this exact question, forecasters broadly work from shared methods, and nobody profits from the club's choice. All three checks pass, so this appeal is good inductive evidence. The course discusses this contrast case and never keys it.

In words: the actor's word fails because it comes from outside the field, while the forecast passes because it is relevant expertise on a question in its own field, offered without a conflict of interest.

Notice that a good appeal to authority is inductive, the kind of argument Week 3 called strong rather than valid. Forecasters can be wrong about a storm. Their forecast still makes the conclusion likely, and that is what a strong argument does.

Misconception check — any appeal to an expert is a fallacy. Students often decide that "trust the experts" is always a fallacy because the Latin name sounds like an accusation. That is tempting, because the catalog lists the appeal to authority among the fallacies. But relevant, agreed expertise with no serious conflict of interest is good evidence, and refusing it would make you worse at reasoning, not better. The fallacy is the unqualified appeal.

Memory hook: right field, broad agreement, no stake.

7. Trace the names: Locke and the ad arguments

You may have noticed the Latin. Ad hominem, ad populum, ad verecundiam: these names have a history, and one book sits near its start.

Locke (1690), An Essay Concerning Human Understanding, Book IV, Chapter 17, named the ad verecundiam and ad ignorantiam arguments and recorded ad hominem as a name already in use. He set all three against ad judicium, the argument from the evidence itself. So Locke's chapter sorts arguments into four kinds: three that lean on something other than the evidence, and one that rests on it.

Worked example — Locke's meaning and the modern one. Compare the two uses of "ad hominem."

Locke's meaning. For Locke, an ad hominem argument pressed someone with the consequences of their own principles or concessions: "you already granted this, so you must accept that." That kind of move can be fair in a debate, because it holds people to what they have said.
The modern meaning. In this course, the attack on the person (ad hominem) rejects a claim because of a fact about the person who made it. The treasurer's old math grade is the modern kind.
The tally of names this week. Locke gave the course two of its Latin names, ad verecundiam and ad ignorantiam, and recorded a third, ad hominem, as already in use. Ad ignorantiam, the appeal to ignorance, waits until Week 13.

In words: the name ad hominem is older than its modern meaning, and Locke used it for holding someone to their own principles, which is different from the attack on the person you identify this week.

Misconception check — Locke invented all the Latin names. Students often credit Locke with inventing ad hominem. That is tempting, because his chapter is the classic place where the names appear together. But Locke recorded ad hominem as a name already known, and he named ad verecundiam and ad ignorantiam himself. Keep the year, 1690, and keep the two meanings of ad hominem apart.

A limitation worth naming: the catalog of fallacies keeps changing. Philosophers still argue about how best to define several of these names and about whether some belong on the list at all. That is one more reason the course keys only clear, neutral passages and leaves borderline cases to discussion.

Memory hook: Locke, 1690: two names his own, one already in use.

Key terms

fallacy — A flaw in the reasoning that connects an argument's premises to its conclusion, so that the premises fail to support the conclusion even when they are true. (first used: 1. Test the link: fallacy versus false premise)
false premise — A premise that is not true, a flaw in an argument's content rather than in its reasoning; an argument can have a false premise and still be valid. (first used: 1. Test the link: fallacy versus false premise)
fallacy of relevance — A fallacy whose premises, even if true, do not bear on whether the conclusion is true, such as an insult, a feeling, or a head count offered in place of reasons. (first used: 1. Test the link: fallacy versus false premise)
attack on the person (ad hominem) — The fallacy of rejecting a claim or argument because of a fact about the person who made it rather than because of the reasons offered. (first used: 2. Answer the reasons, not the person: attacks on the person)
you-too (tu quoque) — The version of the attack on the person that dismisses advice or criticism because the adviser does not follow it, as if inconsistency made the advice unsound. (first used: 2. Answer the reasons, not the person: attacks on the person)
circumstantial attack on the person — The version of the attack on the person that dismisses a claim because of the arguer's situation or interests, such as what they sell or stand to gain, instead of checking the reasons. (first used: 2. Answer the reasons, not the person: attacks on the person)
conflict of interest — A situation in which a person stands to gain or lose from what others believe, such as a paid spokesperson; it is a reason to weigh their testimony with care, not a refutation. (first used: 2. Answer the reasons, not the person: attacks on the person)
testimony — A report by a person that something is so, offered for others to rely on; its weight depends on the person's expertise, track record, and independence from the outcome. (first used: 2. Answer the reasons, not the person: attacks on the person)
straw man — The fallacy of answering a weaker or distorted version of the opposing position instead of the position actually stated, so the reply knocks down a view nobody holds. (first used: 3. Answer the real view: the straw man)
appeal to fear — The fallacy of offering fear of a bad outcome in place of evidence that the conclusion is true, as when an ad warns of disaster instead of showing that its product works. (first used: 4. Weigh the feeling: appeals to fear, pity, and popularity)
appeal to pity (ad misericordiam) — The fallacy of offering sympathy for someone's situation or feelings in place of reasons that bear on whether the conclusion is true. (first used: 4. Weigh the feeling: appeals to fear, pity, and popularity)
appeal to popularity (ad populum) — The fallacy of offering the number of people who believe something in place of reasons that bear on whether it is true. (first used: 4. Weigh the feeling: appeals to fear, pity, and popularity)
red herring — The fallacy of changing the subject to a different issue and treating the new issue as if it settled the original one. (first used: 5. Stay on the question: the red herring)
appeal to authority — An argument that a claim is true because an authority says so; it is good inductive evidence when the authority has relevant expertise, experts broadly agree, and no serious conflict of interest exists. (first used: 6. Check the expert: appeals to authority)
appeal to unqualified authority (ad verecundiam) — The fallacy of resting a claim on an authority when relevant expertise, expert agreement, or independence is missing, most often when the authority speaks outside their field. (first used: 6. Check the expert: appeals to authority)

Summary

A fallacy is a flaw in reasoning; a false premise is a flaw in content.
The relevance test asks whether a premise, if true, would bear on the conclusion.
The attack on the person, the you-too, and the circumstantial attack answer the speaker instead of the reasons.
A documented conflict of interest is relevant to how much you trust testimony, never a refutation by itself.
A straw man answers a view nobody stated; map the real objection first.
Fear, pity, and popularity are fallacies when they replace reasons, not when emotion fits good reasons.
A red herring changes the subject; hold the answer to the original question.
Relevant, agreed expertise with no serious conflict of interest is good inductive evidence.
Locke (1690) named ad verecundiam and ad ignorantiam and recorded ad hominem as already in use.

Check your understanding

Work these before looking at the answers — they are ungraded, and the answers (with reasoning) are at the bottom of the page.

A hiker argues (illustrative): "All mushrooms in this forest are safe to eat. This is a mushroom from this forest. So it is safe to eat." Suppose the first premise is false. Does the argument commit a fallacy, have a false premise, or both?
A neighbor says (illustrative): "The mechanic told me my brakes need new pads, but he's rude to everyone, so I'll skip it." Name the fallacy and say what the neighbor should check instead.
A smoothie shop's sign reads (illustrative): "Over a thousand customers a week can't be wrong: our green smoothie is the healthiest drink in town." Name the fallacy and say what kind of evidence would bear on the conclusion.
A podcast host who is a famous chef says (illustrative), "This laptop is the most reliable one you can buy." A computer-repair technician who has fixed hundreds of laptops says the same thing. Which appeal to authority is stronger, and which check does the weaker one fail?

Answers (worked reasoning — read after attempting)

A false premise, not a fallacy. The form is valid: if all the forest's mushrooms were safe and this is one of them, it would have to be safe. The flaw is in the content, since the first premise is false. The argument is valid but not sound, which is exactly the line between a fallacy and a false premise.
The attack on the person (ad hominem). Whether the mechanic is rude does not bear on whether the brake pads are worn. The neighbor should check the reasons: ask to see the pads, or get a second opinion from another mechanic.
The appeal to popularity (ad populum). A count of customers shows the smoothie sells well, not that it is the healthiest drink. Evidence that would bear on the claim is its nutrition information compared with other drinks, judged against what health experts recommend.
The technician's appeal is stronger. The chef fails the first check, relevant expertise: cooking is not expertise in laptop reliability. The technician has relevant experience with this exact question, though even that appeal is inductive and could be wrong.

Next up in this module: the lecture, the slide deck, the Readings & Resources page, the lecture tutorial, and the practice set. Next week, in Midterm Review & Exam, the review sorts every test so far by the one distinction it asks for, and the fallacy test adds the fallacies of presumption.

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