Free Prep Course > Logical Reasoning > LSAT Assumptions

Is the text an argument? An argument here doesn’t mean a dispute or controversy. It is an attempt to show that something is true, or probably true, by employing something else — facts, assumptions, and/or reasoning — that seems to provide evidence that it is true.

CHALLENGE: Identify the Assumptions

In the prior chapter we discussed the structure of arguments of premises and conclusions in arguments. Assumptions are slightly more complicated. While the conclusion and the premises are stated in the argument, assumptions are not. Assumptions are implicit premises or ideas taken (or “assumed”) to be true but not directly stated.

In many of the Logical Reasoning questions, there will be something bridging the space between the premises and the conclusion. This bridge is what we call the assumptions.

Premise(s) + Assumption(s) = Conclusion

Assumption questions are extremely common and have stems that look like these:

  • Which of the following most accurately states a hidden assumption that the author must make in order to advance the argument above?
  • Which of the following is an assumption that, if true, would support the conclusion in the passage above?
  • Which of the following, if added to the passage, would make the conclusion logical?
  • The validity of the argument depends on which of the following?
  • Upon which of the following assumptions does the author rely?
  • The argument presupposes which one of the following?

How to beat Assumption Questions:

  1. More than simply “putting it in your own words,” you need to evaluate an argument’s persuasiveness. The more unstated assumptions or logical flaws there are, the weaker the argument will be.
  2. Look for gaps between the premises and the conclusion. Go on an Assumption Hunt. What ideas or words are in the conclusion, but not stated in any premise or evidence? That’s an assumption.
  3. Ask yourself why the conclusion is valid. Before you progress to the answer choices, try to get a feel for which assumptions are necessary to fill the gaps between the premises and the conclusion.
  4. Take note of sweeping language or extreme statements.

The Assumption Hunt

The presence of an implicit assumption means that the author’s conclusion will depend upon the strength of the implicit assumptions. We call this search for hidden gaps in reasoning the Assumption Hunt. Many LSAT questions contain hidden assumptions, and it’s your job to find them. The place to find them is hidden between the premises and the conclusion.

Hunt assumptions between premises and conclusions

Here are some of the common keywords for premises and conclusions (we rehash this list many times in the course). Of course there are no keywords for assumptions since they are unstated.

Premise indicators:

The reason is that premises are indicated by keywords.
Because premises are indicated by keywords.
Since premises are indicated by keywords.
As premises are indicated by keywords.
On the basis of premises indicated by keywords.
It follows from premises indicated by keywords.
In view of premises indicated by keywords.
We may infer from premises indicated by keywords.

Conclusion indicators:

Accordingly, conclusions are easy to find.
Clearly, conclusions are easy to find.
Consequently, conclusions are easy to find.
This indicates that conclusions are easy to find.
Hence, conclusions are easy to find.
It follows that conclusions are easy to find.
So, conclusions are easy to find.
Therefore, conclusions are easy to find.
This indicates that conclusions are easy to find.
This shows that conclusions are easy to find.
Thus, conclusions are easy to find.
We may infer that conclusions are easy to find.

Valid vs. True

A valid argument follows from its premises.

P: An ostrich is a bird
P: All birds fly
C: An ostrich can fly

The above argument is valid though not true. You should not bring external knowledge to the LSAT — your job is to search for arguments that are valid given the premises provided in the question.

Why are flying ostriches so important to skilled critical thinking?

The premises the LSAT presents to you will be valid, but the conclusions will often be dodgy. What binds them are the assumptions. So, the crux of many LSAT questions will be the assumptions.

Drill #1

A LSAT course will teach you how to attack the common LSAT question types so that you can beat the LSAT. You should therefore buy a LSAT course.

What assumptions are made in this argument? Think about it creatively and quickly.

Explanation

Premise: A LSAT course can teach you how to attack the common LSAT question types.
Conclusion: You should therefore buy a LSAT course.

In this argument, there is a “gap” between premise and conclusion that is bridged by assumptions. Your job is to assess the strength of those assumptions. Here are some weaknesses in the assumptions :

  1. A LSAT course can teach you common question types, but not all question types. A LSAT course can try to prepare you, but obviously a course can’t prepare you for every past question that has appeared on the LSAT.
  2. The LSAT comes up with new questions all the time, so it is possible that you can come across a question that no one has seen before.
  3. An LSAT course may have the content, but will you have the willpower to use it?

Drill #2

A study released yesterday by the American Dental Association shows that people who gargle with Berry Pop Soda are 20% less likely to get cavities. We should, therefore, stock up on Berry Pop Soda and prepare ourselves for increased demand.

What assumptions are made in this argument? Think about it creatively and quickly.

Explanation

The premise is a new report coming out, and the conclusion is that it would lead to increased sales. That’s quite a leap!

Let’s quickly brainstorm some assumptions:

  1. People know about the study released yesterday.
  2. People believe in the credibility of the study whose results were published yesterday.
  3. The taste of Berry Pop soda is acceptable to people.
  4. There aren’t lots of other sodas available that are more effective at preventing cavities than Berry Pop Soda.
  5. There isn’t a cavity prevention method that is a suitable and/or favorable alternative to gargling with soda.

These predictions will help you wade through the answer choices without getting confused or wasting time!

Drill #3

Apartment building owners argue that rent control should be abolished. Although they acknowledge that this will increase rent prices in the short term, owners argue that in the long term the greater profitability will lead to an increase in the construction of new apartment buildings. Increased apartment construction will then lead to a greater supply of residences and, ultimately, lower rent prices as the increasing supply decreases demand. Thus, abolishing rent control will rapidly reduce prices.

Express this complicated argument in your own words.

Explanation

Premise 1: Abolishing rent control will increase the supply of housing (premise).

Premise 2: Greater supply leads to lower prices (premise).

Conclusion: Abolishing rent control quickly leads to lower rent.

Try to find gaps between the premises and the conclusion.

This is a supply/demand argument; increasing profitability leads to a greater supply which in turn leads to lower prices. However, the link between the chain of evidence and the conclusion is shaky. The property owners’ argument has a lot of “ifs” to begin with and, though we need to accept the evidence chain as factual (premises are always accepted as true), we have to keep in mind that it is worded as an eventual reality, not an immediate outcome. The conclusion, therefore, assumes that the outcome is guaranteed, firstly, and, more importantly, going to happen rapidly.

https://youtu.be/_HxvVaBqa08

Sample Question

Since the late 1970s and early 1980s, tax incentives and other changes have encouraged increasing numbers of venture capitalists and entrepreneurs to start new enterprises. Since 1980, some one-half million new ventures have been started. Not all have succeeded, of course.

The above statement makes which of the following assumptions?

(A) Success in starting a new business depends in large part on sound financial planning.
(B) Social incentives motivate investors just as much as financial rewards do.
(C) Financial incentives are associated with new business starts.
(D) Most new business ventures succeed initially but fail later on.
(E) Venture capitalists are motivated by non-monetary gains.

 

Explanation

Explanation:

This is an “after this, therefore, because of this” argument. It assumes that tax changes since the 1980s have led to an increase in the number of small businesses.

(A) may be true, but there is nothing in the passage to substantiate it.
(B) may be true, however the passage does not allow for social motives to be imputed to investors, let alone that they are as strong as financial motives.
(C) is the correct answer.
(D) can be eliminated because of the word “most”.
(E) is not supported by any evidence in the passage.

Negation Test for Assumption Questions
To test if a statement is an assumption required for an argument, try to negate it. If the argument falls apart, it means that the argument requires that assumption.

In the above sample question if you got rid of the assumption that people are motivated by financial gain, then the argument falls apart. Therefore, that assumption is likely necessary for the argument.