Volume II: Logical Reasoning · Chapter 21
The job: Read It or Fix It. Match a broad rule to the case it governs, or pick the rule that justifies an argument.
Frequency: roughly 2 to 3 per section. Difficulty: medium, with a hard tail in justify mode.
A principle is a broad rule that maps situations to judgments or actions. “Anyone who knowingly profits from a fraud shares the blame for it.” “A policy is fair only if it treats similar cases alike.” Each takes a class of situations and tells you what follows: a verdict, a duty, a choice. That is all a principle is, a general statement with reach beyond any single instance.
Principle questions are not a type of their own. They are an overlay the test bolts onto types you already know. A principle stem can sit on top of a Must Be True question, a Strengthen question, even a Cannot Be True question. So your first job when you see the word “principle” is not to reach for a special method, it is to ask which underlying job the stem is giving you. Almost always it is one of two, and this chapter teaches both.
In apply/conform mode, you are handed a principle and asked to find the case it governs. This is a Read It job (Chapter 8, Must Be True): you accept the rule and hunt for the answer it covers cleanly. In justify/strengthen mode, you are handed a flawed little argument and five candidate rules, and you pick the rule that, added to the facts, supports the conclusion. This is a Fix It job, first cousin to Sufficient Assumption (Chapter 12) and Necessary Assumption (Chapter 11). The principle plays the part of the bridging assumption.
Get the mode right and these questions are routine. Get it wrong and you apply the wrong method to the right stimulus. Read the stem deliberately, decide the mode, then proceed.
The tell is the word principle, or a synonym: proposition, precept, policy, generalization, standard. The mode is fixed by the verb.
Apply/conform mode (you have the rule, find the case):
Justify/strengthen mode (you have the argument, find the rule):
Watch the direction. If the single rule is in the stimulus and the cases are in the answers, you are in apply mode. If the argument is in the stimulus and a different rule sits in each answer, you are in justify mode. That structural difference beats any single keyword.
Decide before you touch the stimulus: is the rule given to me (apply), or am I choosing among rules (justify)? Everything downstream depends on this.
Most principles are conditionals in disguise. “A reviewer should disclose any gift from a company whose product she reviews” becomes received gift from reviewed company → must disclose. Diagram it the way you learned in Chapter 3. Note the trigger (the sufficient condition) and the outcome (the necessary condition). If the principle carries a caveat (“unless the gift is worth less than ten dollars”), fold that in too.
Sometimes the principle is not stated but illustrated by a scenario, and the stem says “the principle illustrated above.” Then your first move is to extract the rule, exactly as you would generate a bridging assumption: ask what general rule would make this specific judgment correct, pulled to the right level of generality. Then proceed as if it had been stated. In everyday terms: you watch a manager send one worker home for showing up without the required safety boots, and you infer the unstated rule, no boots means no shift. You pulled the general policy up from a single ruling, which is the extraction move exactly.
The right answer satisfies the trigger and shows the outcome, or it matches the contrapositive. Do not evaluate the scenario for flaws here. You are matching a case to a rule, not auditing an argument.
This is assumption work. Isolate the conclusion and the premises (the Therefore Test, Chapter 2). Find the term or scope that appears in the conclusion but is missing from the premises, just as you do for Necessary and Sufficient Assumption. The correct principle is the broad rule that bridges that gap.
Two things to hold onto. First, a correct principle can be broader than the case and still be right. A rule about “any public official” will justify a conclusion about one mayor. Do not reject a principle for being general; that breadth is how it covers the case. Second, do not reject a principle because you personally disagree with it. “If valid” means you grant the rule. Your job is whether it supports the conclusion, not whether it is true.
Borrow this from the parse-and-match technique. A principle usually has more than one piece: a core rule plus a condition or caveat. Split it into parts. Every part must correspond to something in the argument or the case. The best answer accounts for all components and the relationship between them. An answer that nails the rule but ignores the caveat (or matches the caveat but mangles the rule) is wrong. Most wrong answers match some parts and fail on the rest.
Read all five. Knock out reversals, negations, scope creep, and subject-matter lookalikes (see below). Confirm the survivor accounts for every part.
A consumer-protection guideline holds that a business may advertise a product as “new” only if the product differs from the business’s previous offerings in a way that affects how the product performs. A purely cosmetic change does not qualify.
Which one of the following judgments most closely conforms to the guideline above?
(A) A bakery that has changed only the shape of its long-selling crackers, leaving the recipe untouched, may nonetheless advertise the crackers as “new” because customers will perceive them differently.
(B) A software company that rewrote its app’s code so the app runs twice as fast, with no change to what the app looks like or does, may advertise the app as “new.”
(C) A shampoo maker that changed its bottle’s color but nothing else may not advertise the shampoo as “new,” and this shows the guideline is too strict.
(D) A car manufacturer that added a more powerful engine to an existing model may not advertise the car as “new,” because the body is unchanged.
(E) A juice brand that switched to a sweeter formula may advertise the juice as “new” only if it also redesigns the label.
Translate the rule: advertising as “new” requires a difference that affects performance, advertise "new" → performance-affecting difference. Cosmetic-only changes fail. Contrapositive: no performance-affecting difference → may not advertise "new". Now match.
(B) is correct. Running twice as fast affects how the product performs, so advertising it as “new” conforms. Every part lines up: a real change, and one that bears on performance.
(A) is wrong. A new cracker shape with an untouched recipe is cosmetic, so the rule forbids “new,” but (A) permits it on the basis of customer perception, which the rule never mentions. It reverses the rule’s verdict.
(C) is wrong. Its judgment is correct (a color change is cosmetic, so “new” is barred), but it tacks on “this shows the guideline is too strict.” In apply mode you do not critique the principle, you apply it. The editorializing breaks the match.
(D) is wrong. A more powerful engine affects performance, so the rule permits “new.” (D) forbids it, citing the unchanged body, importing an extra necessary condition (the body must change) the rule does not contain.
(E) is wrong. A sweeter formula affects performance (taste is how a juice performs), so the rule already permits “new.” (E) makes the label hinge on a label redesign, an extra necessary condition the principle never imposes. Same trap as (D).
A city councilor argues: The proposed riverside park would be enjoyed mainly by residents of the wealthy neighborhoods that border the river, yet it would be paid for out of citywide taxes collected from everyone. Therefore the city should not build the park.
Which one of the following principles, if valid, most helps to justify the councilor’s reasoning?
(A) A city should fund a public project only if a majority of residents say they would use it.
(B) A city should not fund a public project whose benefits would flow mainly to a group narrower than the group bearing its costs.
(C) A city should build parks wherever doing so would raise nearby property values.
(D) A city should distribute its parks evenly across all neighborhoods, rich and poor alike.
(E) A city should never raise taxes to fund recreational facilities.
Find the gap. The premises give two facts: benefits go mainly to wealthy riverside neighborhoods, costs are borne by everyone. The conclusion: do not build it. Nothing in the premises yet says a mismatch between who benefits and who pays is a reason not to build. That is the missing rule.
(B) is correct. It states exactly the bridge: do not fund a project whose benefits flow mainly to a group narrower than the group paying. Plug it in and re-read. The riverside neighborhoods are narrower than the tax-paying city, the rule forbids funding, the conclusion follows. It is broader than this one park, and that is fine. A rule covering “any public project” still justifies a verdict about this park.
(A) is wrong. It keys funding to whether a majority would use the project. The argument never says what share of residents would use the park, only who would mainly enjoy it and who would pay. With no premise about majority usage, this rule cannot connect to the facts.
(C) is wrong. It points the other way: building parks where they raise property values is good, and the wealthy riverside has the highest values, so the rule would favor building. That supports the opposite conclusion, a standard justify-mode trap.
(D) is wrong. Even-distribution sounds adjacent, but the argument’s stated reason is the benefit-versus-cost mismatch, not geographic evenness. (D) matches the subject matter (parks, neighborhoods) without matching the rule actually used. Parse and match: the premise about who pays has no counterpart in (D).
(E) is wrong. A flat ban on tax-funded recreation would block this park, but for a reason the councilor never gave (he objects to the cost mismatch, not to recreational spending as such), and it uses neither premise about who benefits versus who pays. A principle that reaches the verdict by ignoring the argument’s actual reasoning does not justify that reasoning.
For each, decide the mode first, then choose the best answer.
1. Principle: A teacher should lower a student’s grade for late work only if the lateness was within the student’s control. Which judgment conforms?
(A) A teacher lowers a grade because the student submitted late after oversleeping.
(B) A teacher lowers a grade because the student submitted late after a documented power outage knocked out the school’s servers.
(C) A teacher refuses to lower a grade for a student who was late because he chose to attend a concert.
2. Argument: This medication relieved symptoms in 90 percent of patients in the trial, so the clinic should prescribe it. Which principle, if valid, most helps to justify the conclusion?
(A) A clinic should prescribe a medication only if it has no side effects.
(B) A clinic should prescribe a medication if it relieved symptoms in a large majority of trial patients and no better option exists.
(C) A clinic should prescribe whichever medication is least expensive.
3. Principle: One is obligated to keep a promise unless keeping it would cause serious harm to an innocent person. Which judgment conforms?
(A) Mara promised to lend her car to a friend; she keeps the promise even though doing so leaves her without transport to a routine errand.
(B) Devi promised to reveal a coworker’s location to a man who, she later learns, intends to harm the coworker; she keeps the promise anyway.
(C) Sam promised to attend a party but skips it because he would rather rest.
4. Argument: The new bridge tolls fell hardest on low-income commuters, who can least afford them; therefore the tolls are unjust. Which principle most helps to justify this?
(A) A policy is unjust if its heaviest burdens fall on those least able to bear them.
(B) A policy is just if it raises revenue efficiently.
(C) A policy should be repealed if a majority opposes it.
1. Apply mode. (A) is the cleanest conforming choice. Translate: lower grade → lateness within student's control. (A) Oversleeping is within the student’s control, so lowering the grade satisfies the rule. (B) A power outage is outside the student’s control, so the rule forbids lowering the grade, yet the teacher does, violating the principle. (C) The concert was within the student’s control, so the rule permits lowering the grade; the teacher declines, which “only if” allows (a permission, not a requirement), so (C) is defensible but rests on a subtler reading. (A) is the clean trigger-then-outcome match.
2. Justify mode. (B) is correct. Gap: from “relieved symptoms in 90 percent” to “should prescribe.” (B) bridges it (large-majority relief plus no better option yields “prescribe”), and the conclusion follows. (A) demands no side effects, an extra necessary condition the facts never address. (C) keys the decision to price, never mentioned, and could justify a different drug. (B).
3. Apply mode. (A) conforms. Translate: promise made → keep it, caveat unless keeping it seriously harms an innocent person. (A) Keeping costs Mara only minor inconvenience, no serious harm; the caveat does not fire, so she is obligated and keeps it. Both parts match. (B) Keeping the promise leads a man to harm the coworker, an innocent; the caveat fires, the obligation lifts, she should not keep it, yet she does (matches the rule but ignores the caveat, the parse-and-match trap). (C) “Would rather rest” is not serious harm, so the caveat does not fire and Sam is obligated; skipping violates the rule. (A).
4. Justify mode. (A) is correct. Gap: from “heaviest burden falls on those least able to afford it” to “unjust.” (A) supplies that bridge and is broader than this toll, which is fine. (B) calls efficient revenue-raising “just,” the opposite direction. (C) keys justice to majority opposition, never mentioned. (A).
Put it to work: drill Principle questions in the practice platform, free during early access, with every answer choice explained.
