Inference and Resolution in LSAT Logical Reasoning

Must Be True

What it is

A Must Be True question asks you to identify a statement that is logically guaranteed by the information in the stimulus. If the stimulus were true, the correct answer would have to be true as well—no extra assumptions allowed.

These are sometimes called inference questions. The key mindset is that you are not judging what’s plausible or common sense—you are asking what is forced by the given facts.

Why it matters

Must Be True questions train one of the most fundamental LSAT reasoning skills: drawing valid consequences from stated information. This is the same skill you use when you:

  • notice what a set of premises implies,
  • spot constraints that limit what can be the case,
  • translate conditional or quantified statements into what follows.

This is also the foundation for related tasks:

  • Cannot Be True is essentially the flip side—spot what is ruled out.
  • Most Strongly Supported uses similar reading and inference skills, but with a lower standard of proof.

How it works (the mechanism)

A Must Be True question is best approached as a proof task: can you prove the answer from the stimulus?

Step 1: Separate facts from interpretations

Treat the stimulus as a set of facts (even if they’re about opinions). Your job is to combine them carefully.

A common trap is to “fill in” what seems reasonable in real life. The LSAT punishes that. If it’s not stated or logically implied, you can’t use it.

Step 2: Look for inference-friendly structures

Certain structures generate clean inferences:

  • Conditional statements: “If A, then B.” From these, you can often infer contrapositive: “If not B, then not A.”
  • Quantifiers: “All,” “most,” “some,” “none.” These constrain what must exist or must not exist.
  • Comparisons: “More than,” “at least,” “only,” “the only.” These create ordering or exclusivity.
  • Multiple premises about the same group: two facts about the same set often combine into a necessary overlap or exclusion.

You don’t need to diagram everything, but you do need to respect logical force—words like “some” and “most” are not interchangeable.

Step 3: Use a “low bar” prephrase, then prove

For Must Be True, your prephrase should be modest. The correct answer is often a small, carefully worded consequence.

A powerful technique is to ask:

  • “What is the minimum that must be the case if all these statements are true?”
Step 4: Eliminate answers that go beyond the stimulus

Wrong answers often:

  • strengthen the stimulus (“must” where only “might” is supported),
  • add a new relationship not established,
  • reverse a conditional,
  • confuse “some” with “all,” or “most” with “all.”

Must Be True in action (worked examples)

Example 1 (basic set inference)

Stimulus:

All members of the hiking club are trained in first aid. Some members of the hiking club are certified lifeguards.

Question: Which of the following must be true?

Reasoning:

  • “All hiking club members are trained in first aid.” So anyone who is a hiking club member has first aid training.
  • “Some hiking club members are certified lifeguards.” So at least one person is both (hiking club member) and (certified lifeguard).
  • Since that person is a hiking club member, they must be trained in first aid.

Must-be-true inference: Some certified lifeguards are trained in first aid.

Notice how small the conclusion is: it doesn’t say all lifeguards, and it doesn’t say most.

Example 2 (conditional + contrapositive)

Stimulus:

If the museum extends its hours, then attendance will increase. Attendance did not increase.

Question: Which of the following must be true?

Reasoning:

  • Conditional: If extend hours → attendance increases.
  • Given: attendance did not increase (not B).
  • By contrapositive: If not B → not A.

Must-be-true inference: The museum did not extend its hours.

A classic LSAT trap here is picking “If the museum did not extend its hours, attendance did not increase” (that reverses the relationship and is not supported).

Exam Focus

  • Typical question patterns:
    • “Which one of the following is most strongly supported by the statements above?” (Sometimes this phrasing appears for Must Be True–style stimuli; the difference is in how strongly the right answer is supported—see the MSS section.)
    • “The statements above, if true, most strongly support which one of the following?”
    • “Which one of the following can be properly inferred from the statements above?”
  • Common mistakes:
    • Treating a tempting real-world assumption as if it were implied (e.g., assuming causes, motivations, or typical behavior).
    • Confusing sufficient and necessary conditions—especially failing to use the contrapositive correctly.
    • Over-inferring from “some” or “most” (e.g., concluding a universal claim from partial information).

Most Strongly Supported

What it is

A Most Strongly Supported question asks for the answer choice that is best backed by the stimulus, even if it is not guaranteed with absolute certainty.

This is a crucial distinction:

  • Must Be True: the correct answer is logically forced.
  • Most Strongly Supported (MSS): the correct answer is the best-supported option among five—often very likely given the facts, but not always strictly entailed.

You should think of MSS as an inference question with a slightly lower standard of proof.

Why it matters

In real arguments, we often draw conclusions that are reasonable but not deductively certain. MSS questions test whether you can:

  • recognize what the evidence most strongly points toward,
  • avoid overclaiming,
  • compare answer choices by how well each fits the given facts.

These questions are also where LSAT writers reward careful reading and restraint—the right answer is usually the one that stays closest to what’s given.

How it works (the mechanism)

The most reliable approach is: treat MSS like Must Be True at first, then loosen the standard only if needed.

Step 1: Extract the “direction” of support

Ask: “If these facts are true, what do they make more likely?”

Often, the stimulus will suggest a pattern:

  • a correlation that hints at a general trend,
  • multiple examples pointing the same way,
  • a comparison showing one option outperforming another.

But you still can’t add new facts. MSS is not “best story”; it’s “best supported by these statements.”

Step 2: Use answer choices as hypotheses to test

A practical way to do MSS:

  • For each answer, ask: “Do the premises give me strong reason to believe this?”
  • Prefer answers that restate or lightly extend what’s in the stimulus.
  • Be wary of answers that require a missing link.
Step 3: Watch the language of strength

Strength words matter more in MSS than in Must Be True because wrong answers often become wrong by being too strong.

  • Strong: “always,” “never,” “must,” “only if,” “all,” “none.”
  • Moderate: “generally,” “likely,” “tends to,” “usually.”
  • Weak/existential: “some,” “at least one,” “can,” “may.”

MSS correct answers often use moderate or cautious wording unless the stimulus is itself very strong.

MSS in action (worked examples)

Example 1 (trend inference)

Stimulus:

In a survey of 1,000 commuters, those who took public transportation at least four days per week reported lower monthly transportation costs, on average, than those who drove to work every day.

Question: The statements above most strongly support which one of the following?

Reasoning:

The stimulus reports an association in a surveyed group: frequent public transit users reported lower costs on average than daily drivers.

What is strongly supported?

  • A claim about this survey group’s averages is safe.
  • A claim that public transportation causes lower costs is not proven (it could be that lower-cost commuters choose transit).

A strong MSS answer would sound like:

  • “In the survey, average monthly transportation costs were lower for commuters who frequently used public transportation than for commuters who drove daily.”

A tempting but wrong answer would be:

  • “Taking public transportation at least four days per week reduces a commuter’s monthly transportation costs.” (That asserts causation.)
Example 2 (limited generalization)

Stimulus:

Every book in Professor Lin’s syllabus is available as an e-book. Some of the books in Professor Lin’s syllabus are out of print in hardcover.

Question: Most strongly supported?

Reasoning:

From “some syllabus books are out of print in hardcover” and “all syllabus books are available as e-books,” you can strongly support:

  • “Some books that are out of print in hardcover are available as e-books.”

This is actually also Must Be True—sometimes MSS overlaps with MBT when the inference is deductively guaranteed.

How MSS connects to Must Be True

A useful mental model:

  • If you can prove an answer, it’s automatically most strongly supported.
  • If you can’t prove any answer, pick the one that is most consistent with and most encouraged by the facts, while requiring the fewest extra assumptions.

Exam Focus

  • Typical question patterns:
    • “The statements above most strongly support which one of the following?”
    • “Which one of the following is most strongly supported by the information above?”
    • “If the statements above are true, which one of the following is most strongly supported?”
  • Common mistakes:
    • Treating MSS as an invitation to assume missing causal links (“X happened after Y, so Y caused X”).
    • Ignoring strength of language—choosing an answer with “all/never/must” when the stimulus only supports “some/likely.”
    • Choosing an answer that is true in real life but not particularly supported by the given facts.

Cannot Be True

What it is

A Cannot Be True question asks you to find an answer choice that is logically impossible given the stimulus. If the stimulus is true, the correct answer must be false.

This is the negative counterpart to Must Be True:

  • Must Be True: forced in.
  • Cannot Be True: ruled out.

Why it matters

Cannot Be True questions test whether you can use the stimulus as a set of constraints. Many real reasoning tasks work this way: rules and facts eliminate possibilities until only certain outcomes remain.

They also reward disciplined logic because the LSAT will offer answer choices that are merely unlikely or unsupported. Those are not enough. The correct choice must directly contradict what must follow.

How it works (the mechanism)

Step 1: Translate the stimulus into constraints

Treat each premise as a restriction on what can happen.

  • “All A are B” means you can’t have an A that is not B.
  • “No A are B” means you can’t have any overlap.
  • “If A then B” means you can’t have A and not B together.

Often, just rephrasing in plain language makes the impossibility jump out.

Step 2: Use “violation spotting”

For each answer choice, ask:

  • “Would this create a situation the stimulus forbids?”

A powerful lens is to look for:

  • a direct contradiction of a universal statement,
  • a conditional violation (A and not B),
  • a number/quantity conflict (“exactly two” vs. “at least three”).
Step 3: Don’t confuse “cannot be true” with “not necessarily true”

Four answer choices are typically not ruled out—they might be possible even if not supported.

If you find yourself thinking “the stimulus doesn’t say that,” that’s a sign you’re doing a Must Be True test. For Cannot Be True, you need “the stimulus makes that impossible.”

Cannot Be True in action (worked examples)

Example 1 (conditional violation)

Stimulus:

If the company launches the new app this quarter, then it will hire additional customer support staff. The company did launch the new app this quarter.

Question: Which of the following cannot be true?

Reasoning:

  • If launch → hire support.
  • Launch happened.
  • Therefore hiring support must happen.

So what cannot be true? Any answer saying the company did not hire additional customer support staff.

Notice: an answer like “The company hired customer support staff last year” is not ruled out—it could be true or false.

Example 2 (quantifier conflict)

Stimulus:

No residents of Pine Street own a dog. Some residents of Pine Street own a cat.

Question: Which of the following cannot be true?

Reasoning:

  • “No residents own a dog” means: for every Pine Street resident, dog ownership is false.
  • So an answer asserting “At least one Pine Street resident owns a dog” is impossible.

Meanwhile, “Some Pine Street residents own pets” could be true (cats are pets) but is not forced—it depends on whether cats count (they do, but the stimulus already says some own cats, so that one would actually be Must Be True). This illustrates how some answers can be provable while others are merely possible.

How Cannot Be True connects to Must Be True

A helpful way to see the symmetry:

  • To find what must be true, combine constraints to see what is guaranteed.
  • To find what cannot be true, look for any statement that would break a constraint.

In practice, Cannot Be True often feels faster because you can quickly scan for a choice that contradicts a clear rule.

Exam Focus

  • Typical question patterns:
    • “Which one of the following cannot be true?”
    • “If the statements above are true, which one of the following must be false?”
    • “Which one of the following is most strongly contradicted by the information above?”
  • Common mistakes:
    • Selecting an answer that is merely not supported rather than impossible.
    • Missing a conditional violation because you forget the contrapositive or misread “only if.”
    • Overlooking quantifier implications (e.g., treating “some” as “most,” or forgetting that “no” forbids even one exception).

Resolve the Paradox

What it is

A Resolve the Paradox question (often phrased as “explain the discrepancy” or “resolve the apparent contradiction”) gives you a stimulus with two facts that seem inconsistent. Your job is to choose an answer that, if true, makes both facts able to coexist.

Importantly, you are not asked to prove one fact wrong. You are asked to add a missing piece that shows how both can be true.

Why it matters

These questions test a very practical reasoning skill: real-world information is often messy. When two credible reports clash, strong thinkers look for a distinction, hidden variable, or changed condition that reconciles them.

Resolve the Paradox is also a cousin of “strengthen” questions, but with a very specific target: you strengthen the idea that both statements can be true together.

How it works (the mechanism)

Step 1: Clearly state the two sides of the paradox

Before you touch the answers, articulate the conflict in your own words. For example:

  • “Studies show X increases, but the company did Y and X decreased.”
  • “This policy should reduce costs, yet costs rose.”

If you can’t describe the contradiction crisply, you’ll be vulnerable to answer choices that are related but don’t resolve anything.

Step 2: Identify what would have to be true to make them compatible

Common resolution patterns include:

  • Different groups: The two statements are about different populations.
  • Different time periods: Conditions changed over time.
  • Different definitions/metrics: “Cost” measured differently; “success” defined differently.
  • A hidden factor: Another variable offsets the expected effect.
  • A special case/exceptions: The general expectation holds, but this case is unusual.

A useful way to think: the correct answer supplies a bridge—a fact that makes the surprising outcome unsurprising.

Step 3: Check that the answer addresses the specific gap

Wrong answers commonly:

  • explain only one side,
  • restate the paradox,
  • introduce a new claim that doesn’t connect the two facts,
  • weaken the credibility of one statement (that may “attack” the paradox but does not resolve it in the intended LSAT sense unless the question allows that framing).

The correct answer should make you think: “Ah—that’s how both could be true.”

Resolve the Paradox in action (worked examples)

Example 1 (hidden factor)

Stimulus:

A town replaced all of its streetlights with energy-efficient LED lights, which use less electricity than the old lights. However, the town’s electricity bill for street lighting increased after the replacement.

Paradox: LEDs use less electricity, yet the bill went up.

A resolving answer would say something like:

  • After the replacement, the town increased the number of streetlights and kept them on for longer hours.

Why this resolves it:

  • Each light uses less electricity, but the total usage can still rise if there are more lights or longer operating times.

A tempting wrong answer might be:

  • “The LEDs produce brighter light.” Brightness doesn’t explain higher electricity cost unless it changes usage or wattage in a relevant way.
Example 2 (different definitions/metrics)

Stimulus:

A restaurant introduced a new cooking process designed to reduce food waste. After the change, the restaurant reported that the amount of discarded food decreased, but its spending on food supplies increased.

Paradox: Less waste, but higher spending.

A resolving answer would say something like:

  • The restaurant started buying more expensive ingredients, which increased spending even though waste decreased.

Why this resolves it:

  • Waste is about quantity discarded; spending is about cost. Spending can rise if the unit price rises.

Another viable resolution pattern would be demand-based:

  • The restaurant became more popular, so it purchased more total food (even if it wasted a smaller proportion).

How Resolve the Paradox connects to inference questions

Resolve the Paradox is different from Must Be True/MSS/CBT because you are not constrained to what is already implied—you are allowed to add a new fact from the answer choices. But it’s still an evidence discipline task:

  • The right answer is not just any possible explanation.
  • It must be an explanation that fits tightly and targets the contradiction.

In that sense, it resembles picking the best “missing premise” that restores coherence.

Exam Focus

  • Typical question patterns:
    • “Which one of the following, if true, most helps to resolve the apparent discrepancy?”
    • “Which one of the following, if true, most explains the surprising result described above?”
    • “The statements above appear to be in conflict. Which one of the following, if true, resolves the conflict?”
  • Common mistakes:
    • Choosing an answer that explains only one fact (e.g., why bills might increase) without linking it to the other fact (LEDs use less power).
    • Picking an answer that merely restates the paradox in new words.
    • Falling for an answer that is “interesting” but does not affect the relationship between the two conflicting statements.