How to Identify and Solve Weaken Questions on the LSAT

You can usually recognize weaken questions by the way they’re phrased. Common wording includes:

• “Which of the following, if true, most seriously weakens the argument?”
• “Which of the following, if true, would most undermine the author’s reasoning?” 

These cues tell you that your task is to identify an answer choice that introduces doubt about the strength of the conclusion.

To solve these LSAT questions effectively, start by reading the argument closely and identifying both the conclusion and the evidence. Once you have a clear grasp of the reasoning, ask yourself what the author is assuming. 

A good weaken answer will introduce new information that challenges this assumption or suggests that the conclusion doesn’t necessarily follow from the premises. It might point out an alternative explanation, a missing piece of evidence, or a flaw in the logic.

Be cautious with answer choices that are out of scope, irrelevant to the conclusion, or that strengthen the argument. The correct choice will directly affect the logical link between the evidence and the conclusion, making the argument weaker overall.

5 Sample LSAT "Weaken" Questions With Answer Explanations

Here are five sample Weaken questions with a detailed explanation for each answer.

Sample Question #1 

“Scientist: Earth’s average annual temperature has increased by about 0.5 degrees Celsius over the last century. This warming is primarily the result of the buildup of minor gases in the atmosphere, blocking the outward flow of heat from the planet.”

‍Which one of the following, if true, would count as evidence against the scientist’s explanation of Earth’s warming?

(A) Only some of the minor gases whose presence in the atmosphere allegedly resulted in the phenomenon described by the scientist were produced by industrial pollution.
(B) Most of the warming occurred before 1940, while most of the buildup of minor gases in the atmosphere occurred after 1940.
(C) Over the last century, Earth received slightly more solar radiation in certain years than it did in others.
(D) Volcanic dust and other particles in the atmosphere reflect much of the Sun’s radiation back into space before it can reach Earth’s surface.
(E) The accumulation of minor gases in the atmosphere has been greater over the last century than at any other time in Earth’s history.

Answer:

A. The scientist never mentioned pollution, and the origin of the gases isn’t important to her conclusion. This choice tries to mislead you by invoking unrelated ideas like pollution and global warming. But the gases could just as easily come from natural sources.

B. Correct. This choice is effective because it highlights a mismatch in timing between the supposed cause and the observed effect. If the events happened at different times, it's unlikely the proposed cause is responsible, suggesting another factor led to the warming.

C. This is off-topic. A 0.5-degree rise is significant, and it’s doubtful that only a slight increase in solar radiation would cause such a change. Plus, the argument deals with long-term average temperatures. Some years may have more radiation, but that doesn’t explain a steady upward trend.

D. The argument links changes in atmospheric composition to temperature shifts. This option mentions volcanic particles but doesn’t indicate whether their presence has changed over time, so it doesn't address the core issue.

E. This somewhat reinforces the argument. A dramatic rise in minor atmospheric gases would logically boost their warming influence, supporting the scientist’s explanation.

Sample Question #2

“Although video game sales have increased steadily over the past 3 years, we can expect a reversal of this trend in the very near future. Historically, over three quarters of video games sold have been purchased by people from 13 to 16 years of age, and the number of people in this age group is expected to decline steadily over the next 10 years.”

Which one of the following, if true, would most seriously weaken the argument?

(A) Most people 17 years old or older have never purchased a video game.
(B) Video game rentals have declined over the past 3 years.
(C) New technology will undoubtedly make entirely new entertainment options available over the next 10 years.
(D) The number of different types of video games available is unlikely to decrease in the near future.
(E) Most of the people who have purchased video games over the past 3 years are over the age of 16.

Answer:

A. This supports the argument by suggesting that individuals aged 17 and older aren’t likely to reverse the drop in sales.

B. While this might imply waning interest in video games, it’s not directly relevant. The argument focuses on purchases, not rentals, so this detail doesn’t address the main issue.

C. This bolsters the argument. Since video games are a form of entertainment, the availability of other entertainment options could lead to decreased interest in gaming.

D. The specific genres of games aren’t the focus here. The argument concerns overall sales figures, not preferences for certain types of games.

E. Correct. This weakens the concern by indicating a shift in buying behavior: older consumers now account for most game purchases. Therefore, a decline among 13–16-year-olds may not significantly affect overall sales.

Sample Question #3

“A cup of raw milk, after being heated in a microwave oven to 50 degrees Celsius, contains half its initial concentration of a particular enzyme, lysozyme. If, however, the milk reaches that temperature through exposure to a conventional heat source of 50 degrees Celsius, it will contain nearly all of its initial concentration of the enzyme. Therefore, what destroys the enzyme is not heat but microwaves, which generate heat.”

Which one of the following, if true, most seriously weakens the argument?

(A) Heating raw milk in a microwave oven to a temperature of 100 degrees Celsius destroys nearly all of the lysozyme initially present in that milk.
(B) Enzymes in raw milk that are destroyed through excessive heating can be replaced by adding enzymes that have been extracted from other sources.
(C) A liquid exposed to a conventional heat source of exactly 50 degrees Celsius will reach that temperature more slowly than it would if it were exposed to a conventional heat source hotter than 50 degrees Celsius.
(D) Milk that has been heated in a microwave oven does not taste noticeably different from milk that has been briefly heated by exposure to a conventional heat source.
(E) Heating any liquid by microwave creates small zones within it that are much hotter than the overall temperature that the liquid will ultimately reach.

Answer:

A. This doesn’t help. It just reiterates that microwaves can destroy lysozyme. Higher heat means more microwaves, so this still points to microwaves, not heat, as the likely cause.

B. While this shows a way to fix the issue caused by microwaving, it doesn’t explain why the issue happens. It’s not relevant to identifying the cause.

C. If you chose this, you may have misread it as comparing how quickly microwaves and conventional heat warm milk. It doesn’t do that. Instead, it states the obvious: higher temperatures heat things faster. That doesn’t address the argument.

D. Taste is irrelevant. The focus is on the effect of microwaving on lysozyme, not on how the milk tastes afterward.

E. Correct. This highlights a key difference: conventional heating can’t raise milk above its own temperature (say, 50 degrees), but microwave energy might. That suggests heat, not necessarily microwaves themselves, could be the real reason lysozyme is destroyed.

Sample Question #4

“Columnist: Research shows significant reductions in the number of people smoking, and especially in the number of first-time smokers in those countries that have imposed stringent restrictions on tobacco advertising. This provides substantial grounds for disputing tobacco companies’ claims that advertising has no significant causal impact on the tendency to smoke.”

Which one of the following, if true, most undermines the columnist’s reasoning?

(A) People who smoke are unlikely to quit merely because they are no longer exposed to tobacco advertising.
(B) Broadcast media tend to have stricter restrictions on tobacco advertising than do print media.
(C) Restrictions on tobacco advertising are imposed only in countries where a negative attitude toward tobacco use is already widespread and increasing.
(D) Most people who begin smoking during adolescence continue to smoke throughout their lives.
(E) People who are largely unaffected by tobacco advertising tend to be unaffected by other kinds of advertising as well.

Answer:

A. This uses the absolute term "unlikely," while the stimulus discussed a relative change, saying people were "less likely." Someone can still be unlikely to quit, yet more likely than before. So this doesn’t address the main point.

B. This is just a detail about how the restrictions are structured. The argument is focused on the effect of those restrictions, not the legal specifics.

C. Correct. This suggests a possible third factor, such as shifting public attitudes toward smoking, which could explain both the advertising restrictions and the decline in new smokers. That weakens the original argument.

D. The argument is only about people starting to smoke. What happens after someone begins is irrelevant in this context.

E. This doesn't show whether advertising affects attitudes. Mentioning other types of advertising or saying some people are unaffected doesn't help unless we know how many people are influenced by tobacco ads specifically.

Sample Question #5

“A carved flint object depicting a stylized human head with an open mouth was found in a Stone Age tomb in Ireland. Some archaeologists believe that the object was a weapon—the head of a warrior’s mace—but it is too small for that purpose. Because of its size and the fact that an open mouth symbolizes speaking, the object was probably the head of a speaking staff, a communal object passed around a small assembly to indicate who has the right to speak.”

Which one of the following, if true, would most weaken the argument?

(A) The tomb in which the object was found did not contain any other objects that might have been weapons.
(B) Communal objects were normally passed from one generation to the next in Stone Age Ireland.
(C) The object was carved with an artistry that was rare in Stone Age Ireland.
(D) The tomb in which the object was found was that of a politically prominent person.
(E) A speaking staff with a stone head is thought to symbolize a warrior’s mace.

Answer:

A. The presence of other items in the tomb isn’t the focus. However, if no weapons were found, that would support the idea that the object wasn’t a weapon. If many weapons had been found, it might suggest the object in question was one too.

B. Correct. If an object is traditionally passed down through generations, it wouldn't be buried with someone. This suggests the object wasn’t a communal speaking staff, which supports the conclusion.

C. While the object’s rarity might seem important, it doesn’t actually help determine its function. Just being rare doesn’t tell us what the object was used for.

D. A person with political status might be more likely to be buried with an important symbol like a speaking staff. So this doesn’t challenge the argument.

E. Symbolism doesn’t define function. Even if a speaking staff symbolizes a mace, it remains a staff, not a weapon.

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