If the reason that city residents oppose the purchase of the stone edifice is art critics are divided over whether the edifice qualifies as art, and the city councilperson has claimed that the edifice qualifies as art, why it can’t be deduced that the purchase of the edifice should not be opposed?

Bc the city councilperson's focus is not on whether the purchase of the edifice should or should not be opposed, the city councilperson is discussing what qualifies as art and why the edifice does qualify as art

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Course: LSAT > Unit 1

Lesson 6: Logical Reasoning – Articles

Sufficient assumptions | Learn more

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Welcome to sufficient assumptions!

Some questions in the Logical Reasoning section ask you to identify a sufficient assumption—that is, an assumption that would guarantee that a conclusion follows logically from the given support.

How do we recognize Sufficient Assumption questions?

These questions ask you to identify assumptions that would tie arguments together.

Examples

Which one of the following, if assumed, enables the conclusion of the argument to be properly inferred?

The conclusion follows logically from the premises if which one of the following is assumed?

We’re looking for something that would seamlessly connect an argument’s support to its conclusion. For example, let’s say that an argument is structured in the following way:

Conclusion: The upcoming conference will definitely be profitable

because

Support: If at least 50 people register for a conference, that conference is profitable.

What happens if we assume that 49 people registered for the upcoming conference? That doesn’t guarantee that the conference will be profitable.
What happens if we assume that 55 people registered for the upcoming conference? That does guarantee that the conference will be profitable.
Is it too strong of an assumption if we assume that four billion people registered for the upcoming conference? No—that’s perfectly acceptable!

Necessary assumptions need to be true in order for the argument to even have a chance at working, but they don’t guarantee that the conclusion is actually true if the support is true.
Sufficient assumptions don’t need to be true in order for the argument to survive, but they do guarantee that the conclusion is true if the support is true.

In the conference example we outlined above, assuming that four billion people registered for the upcoming conference would be too strong to be necessary, even though it is sufficient. A necessary assumption would be that “at least 50 people registered for the conference”—notice the weaker language that’s required in order to avoid creating an assumption that goes too far.

Let’s work through an actual example together.

Example

Activist: Any member of the city council ought either to vote against the proposal or to abstain. But if all the members abstain, the matter will be decided by the city's voters. So at least one member of the city council should vote against the proposal.

The conclusion of the activist's argument follows logically if which one of the following is assumed?

(A) If all the members of the city council abstain in the vote on the proposal, the city's voters will definitely decide in favor of the proposal.

(B) The proposal should not be decided by the city's voters.

(C) No members of the city council will vote in favor of the proposal.

(D) If not every member of the city council abstains in the vote on the proposal, the matter will not be decided by the city's voters.

(E) If one member of the city council ought to vote against the proposal, the other members should abstain in the vote on the proposal.

You can take a similar approach on these questions as you do on Necessary Assumption, Strengthen/Weaken, and Flaw questions: focus on the gap between the conclusion and the support.

✓ Identify the conclusion and support.

We recommend that for Sufficient Assumption questions, you start by identifying the conclusion and the support—this often makes the gap more visible. It can also be helpful to phrase the argument’s structure as, “The arguer believes that [conclusion], because [support]” in order to detect any jumps in logic or topic.

Conclusion: At least one member of the city council should vote against the proposal

because

Support: Any member of the city council ought either to vote against the proposal or to abstain, but if all the members abstain, the matter will be decided by the city's voters.

✓ Identify any gaps in the argument.

A good next step is to look for a gap between conclusion and support. Gaps are often present in Sufficient Assumption questions, since our task is to fill that gap in with a claim to cement the path from support to conclusion.

The arguer’s conclusion is that someone should vote no to the proposal. Why? Because the only alternative—everyone abstaining—would defer the decision to the voters.

What’s not stated explicitly, but is rather taken for granted? The arguer seems to be assuming that leaving the decision to the voters would be a bad thing. However, that isn’t demonstrated, so the argument is far from airtight.

✓ Diagram if necessary.

Sufficient Assumption questions often include a number of conditional statements. Sometimes, when they appear to link up, or they involve tricky operators like “unless” and “only”, consider diagramming them. While it takes time, it can be a safe and accurate way to home in on the missing relationship.

This argument’s conditionals don’t link, so a diagram may not be very helpful in this case.

✓ Match a choice to your prediction.

We identified a gap between “the voters would decide” in the support and “therefore we shouldn’t let the voters decide” (paraphrased) in the conclusion. A sufficient assumption will completely bridge this gap. Taken together with the support provided, it will enable the conclusion that at least one person should vote against the proposal (and thus not allow the voters to decide).

Top tip: Stronger is often better. It can be helpful to anticipate an answer that provides the missing relationship or information in a fairly strong way. Sufficient assumptions have to guarantee the truth of a conclusion, so it’s often the case that the more strongly they’re phrased, the better.

What would completely bridge the gap in question? The assumption that:

The council should try to avoid an outcome in which the city’s voter’s decide the proposal.

Top tip: The power of prediction. It’s generally easier to predict a sufficient assumption before looking at the choices than it is to predict a necessary assumption. The gap tends to be more visible to readers. So, it’s worth spending extra time on Sufficient Assumption questions to anticipate a specific answer—you can save a lot of time and mental energy on Test Day if you only have to find a match for your prediction, instead of slogging through each choice and giving it more benefit of the doubt than it deserves.

✓ Eliminate strategically.

If you aren’t able to make a prediction—and that will happen sometimes!—don’t be alarmed. It’s time to try to cross out a few choices. You can increase your likelihood of getting the question right by process of elimination. Remember that there’s no penalty for wrong answers on the LSAT, so you should never leave any questions blank.

As a first pass, some students like to look for choices that are irrelevant.

Evaluate the wrong choices on your own, and then compare your evaluations to ours:

(A) If all the members of the city council abstain in the vote on the proposal, the city's voters will definitely decide in favor of the proposal.

This isn’t a sufficient assumption for the argument. Although the arguer recommends that a council member either abstain or vote against, that doesn’t necessarily mean that the arguer’s main fear is that the city’s voters will definitely decide in favor of the proposal—the arguer is pushing against letting the city’s voters even have anything to do with voting on the proposal. Whether the proposal is approved or not isn’t the question.

This choice introduces the idea of what city council members will do, when in fact the issue is what council members should do—by not letting the city’s voters make the decision on the proposal. The way to do that is to make sure at least one of the city council members votes—regardless of which way they vote.

(D) If not every member of the city council abstains in the vote on the proposal, the matter will not be decided by the city's voters.

This choice might sound confusing with the multiple negatives, but it’s not sufficient to establish the passage’s conclusion. We’re told that if every member abstains, then the matter will be decided by the city’s voters. But that’s not logically equivalent to this choice, which is that if not every member abstains, the matter won’t be decided by the city’s voters. It’s logically possible, according to what we’re given, that if someone from the city council votes on the proposal, the city’s voters could still decide the vote.

If you’re struggling with this concept, try working through the article Conditional reasoning and logical equivalence.

(E) If one member of the city council ought to vote against the proposal, the other members should abstain in the vote on the proposal.

This doesn’t connect the argument’s support to its conclusion, because the arguer only recommends that the members either vote against or abstain, but also that at least one person shouldn’t abstain—the concern is with keeping the proposal vote out of the hands of the city’s voters. This choice creates a dichotomy of the way members should vote, that isn’t present in the argument.

✓ Test by affirming.

Remember that the answer to a Sufficient Assumption question—when added to the original argument—guarantees the conclusion will follow logically from the support. In other words, if the sufficient assumption is true, then the conclusion is the logical result of the passage’s support. Note that this isn’t the same as the conclusion being a true statement!

Conclusion: Earth is a bigger planet than Jupiter

because

Support: Earth has oceans.

A sufficient assumption here would be that any planet that has oceans is bigger than Jupiter. Do you see how you probably disagree with the actual truth of the conclusion and the actual truth of the sufficient assumption? That’s okay! Look what happens when we add the support and the assumption together:

Earth has oceans.
Any planet that has oceans is bigger than Jupiter.

What is the logical conclusion to this combination of facts? It must logically follow that Earth is bigger than Jupiter (even though that's not true in real life).

Top tip: Assume that each choice is true and see how it affects the argument. If you add a statement in a choice to the argument’s support and the conclusion becomes guaranteed, then you’ve found a sufficient assumption!

Note: Because of Test Day time constraints, this strategy is best employed in one of two scenarios:

You’re pretty sure you’re looking at the answer, and you want to check it by affirmation.
You’re stuck between two or three choices, and you’ll affirm both to see which of them guarantees the conclusion.

Let’s try it with one wrong choice from our example question as well as with the answer. Here’s the argument outline again:

Conclusion: At least one member of the city council should vote against the proposal

because

Support: Any member of the city council ought either to vote against the proposal or to abstain, but if all the members abstain, the matter will be decided by the city's voters.

No members of the city council will vote in favor of the proposal.
Any member of the city council ought either to vote against the proposal or to abstain, but if all the members abstain, the matter will be decided by the city's voters.

When we combine the support with (A)’s proposed assumption, we cannot draw the same conclusion as the arguer does. The argument is about what members should do, not what they actually do in practice.

(B) The proposal should not be decided by the city's voters.

Any member of the city council ought either to vote against the proposal or to abstain, but if all the members abstain, the matter will be decided by the city's voters.
The proposal should not be decided by the city’s voters.

The deduction here is that all of the members shouldn’t abstain. Since that matches the passage’s conclusion, then (B) is a sufficient assumption.

Summary

✓ Identify the conclusion and support.
✓ Identify any gaps in the argument.
✓ Diagram if necessary.
✓ Match a choice to your prediction.
✓ Eliminate strategically.
✓ Test by affirming if you have time.

Common Incorrect Choices

Not enough: Statements that do help, but not enough to guarantee the conclusion following from its support.
Necessary assumptions: Assumptions that are necessary but not sufficient to guarantee the result.
Not relevant: Information that’s outside of the argument's scope, and thus unable to connect the support to its conclusion.
Backwards: Information that establishes a relationship from the conclusion to the support, instead of from the support to the conclusion.

Your turn

Sufficient Assumptions

A government ought to protect and encourage free speech, because free speech is an activity that is conducive to a healthy nation and thus is in the best interest of its people.

The main conclusion above follows logically if which one of the following is assumed?

(Choice A)
An activity that is in the best interest of the people ought to be protected and encouraged by a nation's government.
(Choice B)
Basic, inalienable rights of the people ought to be protected and encouraged by government.
(Choice C)
An activity that helps a government to govern ought to be protected and encouraged by it.
(Choice D)
A government ought to protect and encourage an activity that is conducive to the interests of that government.
(Choice E)
Universal human rights that are in the best interest of the people ought to be protected and encouraged by a nation's government.

To detect a gap, it can often help to look for what parts seem to “go together” between the conclusion and the support, but aren’t already explicitly connected. The argument might look like this to you, after you’ve searched for these parts:

Conclusion: A government ought to protect and encourage free speech

because

Support: Free speech is an activity that is conducive to a healthy nation and thus is in the best interest of its people.

Notice that “free speech” is already explicitly connected to itself, so it needs no bridge. So we’re essentially told that a government should protect and courage something, because that thing is conducive to a healthy nation and in the best interest of its people.

Can you make a specific prediction using this information?

An assumption that connects the idea from the conclusion and the idea from the support—and therefore closes the gap—could be:

A government ought to protect and encourage any activity that is conducive to a healthy nation or
A government ought to protect and encourage any activity that is in the best interest of its people or

Either one of these assumptions is “enough” by itself to assure the conclusion.

Is there a choice that conceptually matches one of our predictions?

Sufficient Assumptions

City councilperson: Many city residents oppose the city art commission's proposed purchase of an unusual stone edifice, on the grounds that art critics are divided over whether the edifice really qualifies as art. But I argue that the purpose of art is to cause experts to debate ideas, including ideas about what constitutes art itself. Since the edifice has caused experts to debate what constitutes art itself, it does qualify as art.

Which one of the following, if assumed, enables the conclusion of the city councilperson's argument to be properly inferred?

(Choice A)
Nothing qualifies as art unless it causes debate among experts.
(Choice B)
If an object causes debate among experts, no expert can be certain whether that object qualifies as art.
(Choice C)
The purchase of an object that fulfills the purpose of art should not be opposed.
(Choice D)
Any object that fulfills the purpose of art qualifies as art.
(Choice E)
The city art commission should purchase the edifice if it qualifies as art.

Conclusion: [The unusual stone edifice] does qualify as art

because

Support:

The purpose of art is to cause experts to debate ideas, including ideas about what constitutes art itself, [and]
The edifice has caused experts to debate what constitutes art itself.

Note that the first sentence of the passage is really just background information to orient you to the situation. It doesn’t play a part in the argument’s primary components.

Making sure to think of the conclusion as separate from the support, do you notice any gaps in this argument?

What parts seem to “go together” between the conclusion and the support, but aren’t already explicitly connected? The argument might look like this to you, after you’ve searched for these parts:

Conclusion: [The unusual stone edifice] does qualify as art

because

Support:

The purpose of art is to cause experts to debate ideas, including ideas about what constitutes art itself, [and]
The edifice has caused experts to debate what constitutes art itself.

This is a subtle gap that many students accidentally gloss over, because they make the same assumption that the councilperson is making. The gap is between the purpose of art and what qualifies as art.

Can you make a specific prediction using this information?

An assumption that connects the idea from the conclusion and the idea from the support—and therefore closes the gap—could be:

If an object fulfills the purpose of art, then that object does qualify as art or
Any object that accomplishes a purpose of art does qualify as art.

If you didn’t see this on your own because you actually assumed it without realizing it, you can “zoom out” a little and see the gap using this analogy:

If the purpose of moisturizing cream is to hydrate your skin, that doesn’t automatically mean that water (which also hydrates your skin) is a moisturizing cream. It does fulfill the purpose of a moisturizing cream, but it’s water. But if it were to be true that “anything that fulfills the purpose of moisturizing cream does qualify as a moisturizing cream”, then the conclusion would follow that water is a moisturizing cream!

Is there a choice that conceptually matches one of our predictions?

Some final thoughts on Sufficient Assumptions

Note any new info in the conclusion. When the conclusion introduces an important concept that isn’t addressed by the evidence, there’s a good chance the
will appear in the answer—otherwise, the conclusion and evidence would risk not being bridged.
Don’t be scared of strong language in the answer “Overkill” is okay as a sufficient assumption, as long as the assumption is “good enough to get to the conclusion.” In everyday terms, if a pizza costs $20, then $100 would be sufficient (even though it’s more than enough), but it wouldn’t be necessary.
Short on time? Try to eliminate choices, then guess If a question seems too daunting to tackle in the allotted time, consider taking 30-60 seconds to try to eliminate any classic wrong choice types for this question type (irrelevant, too weak, backwards), and any choices that don’t contain key concepts from the conclusion and the evidence.

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hannahsohn99
Posted 3 years ago. Direct link to hannahsohn99's post “Whats the difference betw...”
Whats the difference between necessary and sufficent in the anwser choices?
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sunny890716
Posted 8 months ago. Direct link to sunny890716's post “If the reason that city r...”
If the reason that city residents oppose the purchase of the stone edifice is art critics are divided over whether the edifice qualifies as art, and the city councilperson has claimed that the edifice qualifies as art, why it can’t be deduced that the purchase of the edifice should not be opposed?
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- jocelyn729
  Posted 6 months ago. Direct link to jocelyn729's post “Bc the city councilperson...”
  Bc the city councilperson's focus is not on whether the purchase of the edifice should or should not be opposed, the city councilperson is discussing what qualifies as art and why the edifice does qualify as art
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