Logical Reasoning: Making Arguments Stronger, Weaker, and Testable

Strengthen the Argument

What “strengthening” means on the LSAT

A Strengthen question asks you to pick the answer choice that makes an argument’s conclusion more likely to be true, given the premises. That definition matters because LSAT arguments are rarely “proved” in a strict, deductive way. Instead, most are probabilistic: the premises make the conclusion somewhat plausible, but there’s a gap. Your job is to find new information that helps close that gap.

A common misconception is that strengthening means “add a new premise that, if true, guarantees the conclusion.” That’s usually impossible with the limited, real-world style facts the LSAT gives you. The correct answer typically nudges the argument in the right direction by addressing what the argument is most vulnerable to.

How arguments work: premises, conclusion, and the “gap”

Before you can strengthen anything, you must see the structure.

• Conclusion: what the author is trying to persuade you of.
• Premises: the stated reasons offered to support the conclusion.
• Assumption (gap): an unstated idea that must be true (or at least must hold) for the premises to support the conclusion.

Strengthen questions reward you for spotting the gap quickly. If you can say, “This argument is assuming ___,” you can predict what a good strengthening answer will look like.

A practical strengthening process (what to do on test day)

1. Identify the conclusion (often after words like “therefore,” “thus,” “so,” “hence,” “consequently,” or it may be the author’s recommendation or prediction).
2. Identify the support (premises, evidence, data, examples).
3. Describe the reasoning in one sentence: “Because (premises), the author thinks (conclusion).”
4. Name the gap: What would have to be true for that move to be reasonable?
5. Pre-phrase the type of help needed (not the exact wording): “We need to rule out an alternative cause,” “We need to show the sample is representative,” “We need to show this policy won’t backfire,” etc.
6. Choose the answer that best helps—even if it feels modest.

Common ways LSAT arguments are weak—and how strengthening answers fix them

Strengthening answers tend to fall into a few repeatable “jobs.” Learning these jobs helps you predict correct answers.

1) Strengthening by supporting a key assumption (“bridge the gap”)

Often the argument leaps from one idea to another as if they’re connected. A strengthening answer supplies that missing connection.

Example 1 (bridging an assumption)

Stimulus:
People who drink two cups of green tea daily have lower rates of colds than people who do not. Therefore, drinking two cups of green tea daily reduces a person’s chance of catching a cold.

What’s happening: The premise is a correlation (tea drinkers have fewer colds). The conclusion is causal (tea reduces colds). The gap is that something else might explain the difference.

Which answer would strengthen?
A strong answer would reduce the “something else” concern—e.g., that tea drinkers also sleep more, exercise more, or avoid crowds.

A strengthening statement (illustrative):
Compared with non–green tea drinkers, the green tea drinkers in the study did not differ significantly in sleep, exercise, or exposure to other people.

Why it strengthens: It makes it more plausible that green tea itself is responsible, not a lifestyle confound.

2) Strengthening by ruling out an alternative explanation

This is especially common in causal arguments. If the argument says “A caused B,” the best strengthening often says “It’s unlikely that C caused B” or “B didn’t cause A.”

Key idea: Causal reasoning is fragile. It can be weakened (and therefore strengthened) by alternative causes, reverse causation, or coincidence.

3) Strengthening by shoring up evidence quality

Sometimes the reasoning is fine, but the evidence is questionable.

Common evidence problems:

• Sample representativeness: a survey of 50 volunteers can’t safely represent a city.
• Measurement validity: the test might not measure what it claims.
• Cherry-picking: only favorable cases are presented.

A strengthening answer might say the sample was random, the method reliable, the measurement accurate, or the results replicated.

4) Strengthening by showing the premise is more relevant than it looks

Some arguments use an analogy, comparison, or general principle. A strengthening answer can show the compared cases are truly similar in the relevant ways.

5) Strengthening recommendations by addressing feasibility, side effects, or incentives

When the conclusion is “We should do X,” you should look for gaps like:

• Will X actually achieve the goal?
• Will X create worse problems?
• Will people comply?
• Is there a cheaper/easier alternative?

Strengthening often supports the plan’s effectiveness or blocks predictable obstacles.

Strengthen in action: a worked multiple-choice style example

Stimulus:
A city plans to reduce traffic congestion by increasing the cost of downtown parking. Since higher parking costs will discourage people from driving into downtown, congestion will decrease.

Step 1: Conclusion: Congestion will decrease.

Step 2: Premise: Higher parking costs discourage driving downtown.

Step 3: Gap: Even if fewer people drive downtown, congestion might not fall overall (drivers might circle longer looking for cheaper spots, shift to nearby streets, or congestion might come from through-traffic). Also, people might still drive and just pay.

What would strengthen?

• Evidence that many downtown drivers are price-sensitive and will switch to public transit.
• Evidence that through-traffic is not the main source of congestion.

Correct-answer “shape” (illustrative):
Most drivers who currently park downtown have convenient access to public transit and have said they would use it if parking prices rose.

Why this is the best kind of help: It directly supports the key mechanism: higher cost → fewer cars downtown.

Exam Focus

• Typical question patterns:
  • “Which of the following, if true, most strengthens the argument?”
  • “Which of the following, if assumed, would provide the strongest support…?” (similar skill, slightly more assumption-focused)
  • “Which of the following, if true, most supports the conclusion…?”
• Common mistakes:
  • Picking an answer that is related to the topic but doesn’t affect the specific reasoning gap (topical relevance is not logical support).
  • Overvaluing extreme language (“proves,” “guarantees”)—strengthening is usually incremental.
  • Strengthening a premise you like rather than strengthening the link from premises to conclusion.

Weaken the Argument

What “weakening” means on the LSAT

A Weaken question asks you to pick the answer choice that makes the conclusion less likely, given the premises. Importantly, weakening does not require destroying the argument. You are not looking for something that makes the conclusion impossible—just something that meaningfully undermines the reasoning.

Weaken questions are the mirror image of Strengthen. If strengthening often “patches” the gap, weakening often exposes it—by showing an alternative explanation, an exception, a missing distinction, or a reason the evidence doesn’t support the conclusion.

The weakening mindset: attack the argument’s vulnerability, not its topic

Many wrong answers feel tempting because they disagree with the conclusion or introduce negative-sounding facts. But LSAT weakening is about logic, not attitude.

A good weakening answer typically does one of these:

• Shows the premises can be true even if the conclusion is false.
• Introduces an alternative cause or explanation.
• Shows the evidence is unreliable or unrepresentative.
• Reveals a key assumption is false.
• Shows the plan won’t work (or will backfire) in recommendation arguments.

High-frequency weakening techniques (and what they look like)

1) Provide an alternative explanation (especially for causal conclusions)

If the argument says “A caused B,” a classic weaken is “B is actually caused by C,” or “B causes A,” or “A and B are correlated because of C.”

Example 1 (alternative cause)

Stimulus:
After the company introduced standing desks, employee productivity rose. Therefore, standing desks increase productivity.

Weakening idea: Something else changed at the same time.

A weakening statement (illustrative):
At the same time the standing desks were introduced, the company also changed its bonus policy to reward higher output.

Why it weakens: Productivity might have increased because of incentives, not desks.

2) Show the cause is present without the effect (or the effect without the cause)

Causal claims imply a pattern. If you can show the pattern doesn’t hold, the causal story weakens.

• Cause without effect: “Many who did A didn’t get B.”
• Effect without cause: “Many who got B didn’t do A.”

These don’t have to eliminate the possibility of causation, but they undermine confidence.

3) Attack the evidence: sampling, measurement, comparisons

If the argument relies on a study or survey, weakening often points out:

• The sample is biased (volunteers, unusual subgroup).
• The measurement doesn’t track the claimed phenomenon.
• The comparison group differs in relevant ways.

4) Exploit ambiguity or shifting definitions

A frequent LSAT flaw is subtly changing meaning—like “successful students” meaning “high GPA” in one sentence and “good careers” in the next. A weaken answer can highlight that the evidence supports one meaning but not the other.

5) Introduce a relevant counterexample or limiting condition

If the argument generalizes too broadly, weakening can show an important exception.

Be careful: not every exception weakens. It must be an exception that hits the scope of the conclusion. If the conclusion is already narrow, a broad counterexample might miss.

Weaken in action: a worked multiple-choice style example

Stimulus:
A nutritionist claims that eating breakfast improves concentration in college students. In a study, students who ate breakfast scored higher on a concentration test than students who did not.

Step 1: Conclusion: Eating breakfast improves concentration.

Step 2: Premise: Breakfast-eaters scored higher on a concentration test.

Step 3: Gap: Correlation vs causation; group differences; reverse causation (more conscientious students both eat breakfast and concentrate better).

What would weaken most?
A strong weakening answer would provide a confound.

Weakening statement (illustrative):
Students who ate breakfast in the study also reported getting significantly more sleep on average than students who did not.

Why it weakens: Sleep plausibly explains higher concentration, reducing the need to credit breakfast as the cause.

A subtle but crucial skill: weakening the conclusion, not “attacking” the premise

Sometimes test-takers try to weaken by contradicting a premise. But on the LSAT, answer choices are assumed true. If an answer choice directly contradicts a premise, that would certainly weaken—but LSAT writers often avoid such blunt options. More commonly, you weaken by showing the premises don’t establish the conclusion.

That’s why alternative explanations are so powerful: they let the premise remain true while undermining the inference.

Exam Focus

• Typical question patterns:
  • “Which of the following, if true, most weakens the argument?”
  • “Which of the following, if true, casts the most doubt on the conclusion?”
  • “Which of the following, if true, most seriously undermines the reasoning?”
• Common mistakes:
  • Choosing an answer that is merely in tension with the conclusion’s theme but doesn’t target the reasoning gap.
  • Confusing “weaken” with “present an opposite conclusion.” You can weaken without offering a new conclusion at all.
  • Missing scope: picking an answer that weakens a different claim than the one the argument actually concludes.

Evaluate the Argument

What it means to “evaluate” an argument

An Evaluate question asks for information that would help you judge whether the argument’s reasoning is good—typically by identifying what you would need to know to decide if the conclusion is warranted.

These are different from Strengthen/Weaken questions in an important way:

• Strengthen/Weaken: you are given statements that already push the argument one direction.
• Evaluate: you are asked to pick a statement (often phrased as a question) such that either answer (yes vs no, high vs low, more vs less) would significantly affect how convincing the argument is.

In other words, Evaluate questions are about finding the argument’s pressure point—the uncertain assumption the argument depends on.

Why Evaluate questions matter

Evaluate questions train a core LSAT skill: identifying exactly what an argument is relying on. In real life, this is the difference between arguing productively (“Let’s find out whether the sample was representative”) and arguing emotionally (“That can’t be true!”).

On the exam, Evaluate questions reward you for being precise about what would actually change your mind.

The core mechanism: find the hinge assumption and ask a “yes/no that matters”

Most Evaluate questions can be solved with a reliable approach:

1. Identify the conclusion and premises.
2. Find the gap (the same way you would for Strengthen/Weaken).
3. Turn that gap into a question.
4. Select the answer choice that asks that question—so that a “yes” would strengthen and a “no” would weaken (or vice versa).

This “yes strengthens / no weakens” property is a powerful test. If either answer wouldn’t matter much, it’s probably not evaluating the argument.

What Evaluate stems usually look like

Evaluate question stems often include phrases like:

• “Which of the following would be most useful to know in evaluating the argument?”
• “The answer to which of the following questions would be most relevant to assessing the reasoning?”
• “Which of the following, if answered, would help determine whether the argument is valid/sound/well supported?”

(They may not use the word “valid” in a formal logic sense; treat it as “well supported.”)

Common types of evaluation targets

1) Causal arguments: test alternative causes and direction

If the conclusion is “A causes B,” useful evaluation questions include:

• Were other factors controlled?
• Does B occur without A?
• Does A occur without B?
• Could B cause A?

The key: an evaluate question doesn’t assert a confound; it asks whether a confound exists.

2) Generalizations from samples: test representativeness

If the conclusion generalizes to a population, you often need to know whether the sample reflects that population.

Useful evaluation questions:

• How were participants selected?
• Are key demographics similar?
• Was the response rate low?

3) Plans and recommendations: test effectiveness and unintended consequences

If the conclusion recommends an action, evaluation often asks:

• Will people comply?
• Will it achieve the goal?
• What are the costs/tradeoffs?
• Are there better alternatives?

4) Analogies and comparisons: test relevant similarity

If the argument says “because X worked there, it will work here,” evaluate by asking whether the situations match in the features that matter.

Evaluate in action: worked examples

Example 1 (causal evaluation)

Stimulus:
A town installed brighter streetlights last year. Since then, nighttime crime has decreased. Therefore, installing brighter streetlights reduces nighttime crime.

Conclusion: Brighter streetlights reduce crime.

Gap: Crime could have fallen for other reasons (more police patrols, demographic changes). Also, crime might have shifted to another area or time.

A strong evaluate question (illustrative):
During the same period, did the town also increase nighttime police patrols?

Why it evaluates:

• If yes, the streetlight explanation is less convincing (alternative cause).
• If no, the streetlight explanation becomes more plausible.

Notice how the “yes/no” outcome matters substantially.

Example 2 (plan evaluation)

Stimulus:
To reduce cafeteria waste, a school should eliminate trays. Without trays, students will take less food at once, so less food will be thrown away.

Conclusion: Eliminating trays will reduce waste.

Gap: Students might make more trips and take the same amount, or waste might come mostly from kitchen overproduction rather than student choices.

A strong evaluate question (illustrative):
If trays are eliminated, will students typically make additional trips to take the same total amount of food?

Why it evaluates:

• If yes, the plan’s mechanism is undermined.
• If no, the plan’s mechanism is supported.

Distinguishing Evaluate from Strengthen/Weaken when they feel similar

Evaluate answers often look like strengthening or weakening tools—but phrased as unknowns.

• Strengthen: “The sample was randomly selected.” (assertion)
• Evaluate: “Was the sample randomly selected?” (question)

If you ever feel stuck between two answer choices on an Evaluate question, ask:

• “Would opposite answers to this question lead me to opposite judgments about the argument?”
  If not, it’s probably not the best evaluator.

Common traps in Evaluate questions

1. Irrelevant curiosity: The LSAT may offer something interesting but non-diagnostic. Example: “How much did the streetlights cost?” That matters for budgeting, but it doesn’t evaluate the specific causal claim unless the argument is about cost-effectiveness.
2. A question that only strengthens (or only weakens): If either answer doesn’t change much, it’s not a good evaluation tool.
3. A question that evaluates a side issue: Some arguments contain background claims. Evaluate the reasoning to the main conclusion, not a minor premise.

Exam Focus

• Typical question patterns:
  • “Which of the following would be most useful to know in evaluating the argument?”
  • “The answer to which of the following questions would be most relevant to determining whether…?”
  • “Which question would help to assess whether the reasoning is sound?”
• Common mistakes:
  • Treating Evaluate like Strengthen and picking an answer that would help only in one direction, instead of one where either outcome matters.
  • Evaluating the truth of a premise rather than the support from premises to conclusion.
  • Missing the argument’s real gap (e.g., focusing on a minor detail when the core issue is causation vs correlation).