Strengthen vs. Sufficient Assumption on the LSAT: What Must the Answer Accomplish?

By AccessPrep Editorial · Updated November 10, 2026 · Facts checked November 10, 2026

Every argument and answer choice below is an AccessPrep-created practice item, not an official LSAC question; Larkfield, Brindle Hall and the Halvard Community Garden are invented. The review notes are fictional illustrations, not real student work. The method is a teaching proposal, not a validated study finding. AccessPrep and Lovare share a founder, and Lovare offers paid LSAT instruction and admissions consulting.

A sufficient-assumption answer has to make the conclusion follow: add it to the premises and no way remains for the conclusion to be false. A strengthen answer only has to make the conclusion more likely, so it can leave doubt, remove one objection, or report a trend. That is why the same answer choice can be credited under one stem and rejected under the other. Read the stem before the argument and name the job. Then test sufficient-assumption choices by trying to build a counterexample, and test strengthen choices by asking whether the conclusion is now more likely and whether any other choice does more.

Jump to: Two tests · Method · Building example · Concert example · Matrix · Worksheet · Practice

Who this lesson is for

You chose an answer that plainly helped the argument on a sufficient-assumption question, or you passed over a helpful answer on a strengthen question because it did not prove the conclusion. Both misses come from running the other question’s test.

Success is two habits you can check in review: you name the task from the stem before reading the choices, and you write one line per choice saying whether it makes the conclusion follow, makes it more likely, or does neither, with a concrete counterexample for every sufficient-assumption choice you reject.

The AccessPrep blind-review guide gives a neighboring miss as its example of a useful diagnosis: “I picked an answer that would strengthen the conclusion but was not required for it.” That note concerns a required assumption. This lesson takes the confusion between strengthening an argument and making its conclusion follow, and it assumes the review routine that guide sets out.

Two tasks, two different bars

LSAC includes evaluating additional evidence and identifying assumptions among the skills Logical Reasoning questions assess. Its official sample explanations distinguish improving an argument’s support from supplying information that makes its conclusion follow. We use that distinction here without reproducing an official question.

Sufficient assumption: make it follow. Treat the premises and the choice as true. If you can still describe a situation in which the conclusion is false, the choice fails, however much it helps. A choice can be broader than the particular case: words such as every or no are not automatic reasons to reject it. Still check consistency with the premises, the group covered and the direction of the rule.

Strengthen: make it more likely. Treat the choice as true and ask whether the conclusion is better supported than before. The choice can leave doubt. LSAC’s directions warn that multiple choices can seem responsive and require the best answer. So this test has a second step: compare the survivors. Do not stop merely because one option sounds relevant.

Stem wording is a clue, not the test. In LSAC’s sample set, the strengthen stem says “if true” and the sufficient-assumption stem says “if assumed” and “follows logically”. The discrepancy question there also says “if true”, so that phrase only tells you to accept the choice. Read for what the choice must do to the conclusion.

The two demands are nested. A choice that makes the conclusion follow also makes it more likely, and nothing can strengthen more than that. So when a strengthen question offers a choice that closes the gap completely, that choice wins. The reverse never holds: a choice that only raises the likelihood earns no credit on a sufficient-assumption question.

A third task, kept separate. The sample set also has a question that asks you “to find the assumption required by the argument.” That task asks what the argument depends on; its answer need not make the conclusion follow. This lesson does not teach it; just do not bring a “must this be true?” test to a sufficient-assumption question, where the credited answer can be much stronger than anything the argument requires.

These are tests of reasoning, not shortcuts tied to a section length. Practice them on current official material. LSAC explains the skills and question wording on the pages linked above; its terminology need not become a separate vocabulary drill.

The method: name the task, map the gap, test every choice

Work the steps in order.

1. Name the task from the stem. Write “make it follow” or “make it more likely” before you read the choices.

2. Map the gap. Separate the conclusion from the premises and write one line: what the premises establish, and what the conclusion adds that they do not.

3. Predict. For “make it follow”, write a bridge that runs from what the premises give you to exactly what the conclusion claims. For “make it more likely”, list the kinds of help that would count: a partial bridge, an alternative explanation ruled out, a difference between past cases and this one ruled out.

4. Test each choice, applying these rules in order and taking the first that fits.

   • Make it follow: (S1) if the choice contradicts a premise, reject it; (S2) if, with the premises, it leaves no case in which the conclusion is false, credit it; (S3) otherwise reject it, because a counterexample survives.

   • Make it more likely: (T1) if the choice contradicts a premise, reject it; (T2) if it makes the conclusion follow, it is the top candidate; (T3) if it makes the conclusion less likely, reject it; (T4) if it makes the conclusion more likely, keep it as a candidate; (T5) otherwise reject it, because it has no effect.

5. Confirm or compare. For “make it follow”, check that the credited choice’s condition covers the case in the conclusion and runs toward the conclusion, not away from it. For “make it more likely”, if more than one candidate survives, take the one that gives more reason to believe this conclusion about this case; compare the connection, strength and scope of the evidence. Specificity alone does not decide the answer.

On a sufficient-assumption stem, stop working a choice as soon as you have one concrete counterexample (reject) or a two-line derivation (credit).

Argument 1: one sentence, two verdicts

AccessPrep-created practice item, not an official LSAC question.

Larkfield’s building code requires a wind study for every proposed building taller than four stories. The proposed Merrow Street building in Larkfield would be six stories tall. So the Merrow Street building will not open on its scheduled date.

Version 1. Which one of the following, if assumed, allows the conclusion to be properly drawn?

(A) Larkfield also requires wind studies for some buildings of four stories or fewer that stand near the river.

(B) Most Larkfield buildings that required a wind study in the past decade did not open on their scheduled dates.

(C) Every Larkfield building that did not open on its scheduled date in the past decade had required a wind study.

(D) No Larkfield building that requires a wind study opens on its scheduled date.

(E) No Larkfield building taller than six stories opens on its scheduled date, but most buildings of five or six stories do.

Commit to an answer and write one line per choice before reading on.

Map the gap

The premises establish that Merrow Street is taller than four stories, so the code requires a wind study for it. The conclusion adds that it will miss its scheduled date. Nothing links the two, so the predicted bridge is: any building that requires a wind study misses its scheduled date.

Sufficient-assumption verdicts

(D) is credited. Merrow Street is taller than four stories, so the code requires a wind study for it. (D) says no building that requires a wind study opens on its scheduled date. So Merrow Street does not. No case remains in which the premises and (D) are true and the conclusion is false.

(B) is the trap. Suppose 7 of the 10 past wind-study buildings opened late. (B) is true, yet Merrow Street can be like the other 3: the premises hold, (B) holds, and the building opens on time.

(C) runs the wrong way. It says what late buildings had in common, not what happens to buildings that need a wind study. It stays true in a Larkfield where nearly every wind-study building opened on time, and Merrow Street can be one of them.

(E) misses the case. Its rule covers buildings taller than six stories, and Merrow Street is exactly six. Its second half even says most buildings of Merrow Street’s height open on time.

Version 2: same argument, strengthen stem, one choice changed

Which one of the following, if true, most strengthens the argument? Choices (A), (B), (C) and (E) are unchanged. Only (D) is new:

(D) Larkfield keeps its wind-study reports in a digital archive.

Now (B) is credited. The test is no longer “can the conclusion still be false?” (it can) but “is it now more likely?” A record in which most recent wind-study buildings opened late makes it more likely that one more will. The new (D) says how reports are stored, not whether a building will be late. (E) points against the prediction: most buildings of five or six stories, the group Merrow Street is in, open on time. (C) still runs backward: it does not establish how often buildings needing studies open late. (B) supplies that forward-looking evidence more directly.

Choice (B) is the same sentence in both versions. Its truth can help without proving the conclusion. That is the distinction the pair is built to expose.

Do not overlearn the reversal label. A reversed rule fails as a sufficient bridge when it runs away from the conclusion. That does not mean reversed or associative evidence can never matter to any strengthen question. Here, (C) fits a town where few wind-study buildings run late as well as one where many do; it does not establish the forward rate that (B) supplies. Read the whole argument before assigning a probability effect.

Argument 2: an answer that closes one door

AccessPrep-created practice item, not an official LSAC question.

In each of the past eight years in which the opening-night program of the Brindle Hall concert series featured the hall’s resident string quartet, opening night sold out. This year’s opening-night program features the resident quartet. So this year’s opening night will sell out.

Version 1. The conclusion follows logically if which one of the following is assumed?

(A) Ticket prices for this year’s opening night are no higher than they were for any opening night in the past eight years.

(B) Any opening night of the series that does not sell out has a program that does not feature the resident quartet.

(C) Many people who attend opening night also buy tickets to later concerts in the series.

(D) Any opening night of the series that sells out is followed by an extra performance later in the season.

(E) Brindle Hall has more seats this year than it had in any past year.

The premises establish a pattern in past years and that this year’s program fits it. The conclusion adds that the pattern will hold this year. The gap is the step from “has held” to “will hold”.

Sufficient-assumption verdicts

(B) is credited, though it looks backward. Read it as a rule: if a night does not sell out, the quartet was not on its program. That is the rule “if the quartet is on the program, the night sells out” stated from the other end, with both parts flipped and negated (the contrapositive, which the conditional-reasoning lesson practices). It covers every opening night, this year’s included, and the quartet is on this year’s program, so this year’s night cannot be one that fails to sell out. Compare Argument 1’s (C), which flipped the parts without negating them and so changed the rule’s meaning.

(A) is the trap. Ruling out a price rise removes one way this year could differ from the past. Others remain: a storm on the night, a competing event, a bigger hall. Picture unchanged prices, the quartet on stage and empty seats: every premise and (A) are true, and the conclusion is false.

Version 2: strengthen stem, one choice changed

Which one of the following, if true, most strengthens the argument? Only (B) is new:

(B) This year’s opening night falls on the same evening as a free outdoor concert elsewhere in the city.

Now (A) is credited. An argument from past years is only as good as the match between those years and this one. (A) rules out one likely difference, a higher price, so the past pattern becomes a better guide. It does not rule out every difference, which is why it failed version 1 and why it is enough here.

Copy this task-demand matrix

Each row is a kind of choice from this lesson; the matrix is a study aid, not a complete list of what the LSAT uses. A choice that contradicts a premise (none here does) fails rule 1 of both tests and shares the last row.

Free teaching packet: Download the task matrix, gap maps and blank/worked review sheets. It includes the original practice items and CSV versions. No email required.

Copy this worked answer table

Use one table per missed question, before you reread any explanation. Fill every row, including the choice you picked and the credited one.

Before the answer rows, record the question source and number, the task named from the stem (make it follow or make it more likely), and the gap in one sentence: the premises establish ___; the conclusion adds ___.

Worked rows: the same choice, Argument 1’s (B), under both stems.

Two review notes, before and after

These notes are fictional, written to show the correction, not taken from a real student.

Troubleshooting

When to stop drilling this distinction

Count task-demand misses: misses where your note shows you ran the other task’s test, by crediting a sufficient-assumption choice without trying a counterexample or rejecting a strengthener for not proving the conclusion. Work mixed sets of 10 sufficient-assumption and strengthen questions you have not already reviewed, from official PrepTests (LSAC offers four full PrepTests free through LawHub). Move on when two sets in a row have zero task-demand misses and you named the task before reading the choices on all 20 questions. Come back if a later set of 10 has two or more. Ten questions is a small sample, so treat this as a checkpoint for study time, not proof the confusion is gone. Other misses, such as a misread premise, go in your general error log.

Transfer task: one answer set, two stems

AccessPrep-created practice item, not an official LSAC question.

The Halvard Community Garden assigns plots for the coming season only to members who have paid this year’s dues. Every member who volunteered at the spring cleanup has paid this year’s dues. So every member who volunteered at the spring cleanup will be assigned a plot for the coming season.

(A) In each of the past five seasons, every member who had paid that season’s dues was assigned a plot.

(B) Every member who has paid this year’s dues may vote at the garden’s annual meeting.

(C) No member who has not paid this year’s dues will be assigned a plot for the coming season.

(D) Some members who did not volunteer at the spring cleanup have also paid this year’s dues.

(E) Every member who has paid this year’s dues will be assigned a plot for the coming season.

1. Which one of the following, if assumed, allows the conclusion to be properly drawn?

2. Which one of the following, if true, most strengthens the argument?

3. Suppose (E) were deleted. Which choice would then be credited under question 2, and why would it still fail question 1?

Write your three answers and one line per choice before reading the key.

Answer key

1. (E). Every volunteer has paid; (E) says everyone who has paid will get a plot; so every volunteer will get a plot. (E) reverses the first premise, and that is exactly why the argument needs it: the first premise makes paying a requirement for a plot, not a guarantee of one. If you rejected (E) because Argument 1’s reversed (C) failed, look at direction. (C) ran from the conclusion’s claim (late) back to a premise’s term (wind study); (E) runs from what the premises establish (paid) to what the conclusion claims (a plot). (A) describes past seasons, and the coming season can differ: the same “has held, will hold” gap as Argument 2. (C) restates the first premise. (B) starts from the right group and ends at voting. (D) concerns members who did not volunteer.

2. (E) again. It makes the conclusion follow, and nothing can strengthen more. If you chose (A), you treated “strengthen” as “pick the partial answer”.

3. (A). Five seasons in which every paid member received a plot make it more likely that paid volunteers will receive one this season. It still fails question 1 because this season can differ from the past. (B), (C) and (D) still do nothing for the link from paying to a plot.

Put the two tests into your next review.

Free first step: copy the worked answer table, pull your last five missed sufficient-assumption or strengthen questions, and fill one row per choice, at the level of detail in the worked rows above, before rereading any explanation. Then try the free LSAT Study-Plan Check: five questions about your practice, a downloadable seven-day plan, and no email required.

Optional paid path: if you want a tutor to observe you applying these tests to your own missed questions, explore one-on-one LSAT support or contact AccessPrep. Current programs are offered through Lovare Institut, which shares a founder with AccessPrep. Before committing, confirm who will teach, the scope and number of sessions, and the applicable terms. This lesson does not promise a score increase.

Continue your preparation

• Practice conditional direction and contrapositives

• Find the main conclusion before judging support

• Blind review a timed set and diagnose the decision behind each miss

• Turn one error-log pattern into an observable weekly practice action

• Diagnose a flat LSAT score before adding more hours

• Practice separating a claim from the evidence offered for it

• Build a free seven-day plan with the LSAT Study-Plan Check