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LSAT Conditional Reasoning

Updated: Oct 3, 2023

Conditional reasoning is a concept that appears in every LSAT section, and mastering this skill can help you improve your score significantly. For some questions, an understanding of conditionality doesn't just help with your LSAT prep, it's necessary. If you have been struggling with In/Out games, Sufficient Assumption, or Must be True questions, there is a good chance you are struggling with conditional reasoning.


There are many factors to consider when it comes to LSAT conditionality, but for now let's dive into a brief introduction on this topic...




 

What is a Conditional Statement?


Imagine your friend said they would do you a favor on one condition. Does this tell you about anything that has happened? If you said, "No" you are correct! We don't know whether your friend has, will, or is doing you any favor, and we don't know whether his condition has been met. It only tells us what would happen in specific circumstances.


This is ultimately how we can define conditional statements, and this is what differentiates them from most other statements on the LSAT. They are statements that tell us what would happen if certain conditions are satisfied.


Conditional statements are always comprised of two main parts--the sufficient condition and the necessary condition. Let's break down these two conditions, because they have some important differences.


Think about the dictionary definition of "sufficient". "Sufficient" means enough. In other words, the sufficient condition is enough for the necessary condition to occur. If the sufficient condition occurs, the necessary MUST occur. In other words, the sufficient condition cannot occur on its own.


Now, let's consider the necessary condition. "Necessary" means required. So, the necessary condition is a requirement for the sufficient to occur. But requirements do not allow us to conclude the other condition has occurred. For example, a requirement for voting is that you must be a citizen. Does this mean if you are a citizen you are eligible to vote? Not necessarily, because you might not have satisfied other requirements for voting. Maybe you are not old enough to vote, for example. Therefore, it is possible for the necessary condition to occur on its own.


In short, the sufficient condition CANNOT stand on its own, because it must occur alongside the necessary. However, the necessary condition CAN (but does not necessarily have to) stand on its own. More on this later.



 

Identifying Conditional Statements


The most common way for conditional statements to be introduced is through the terms "if" (indicating the sufficient) and "then" (indicating the necessary). Consider the following example statement:

"If you study for the LSAT, you will get a 180"



Is this true in real life? Not necessarily (I hate to be the bearer of bad news). There are plenty of people who studied but did not score a 180. However, this doesn't matter on the LSAT. Don't bring in your outside knowledge. If this is what was stated in the passage, you will typically need to accept it as true. In most passages, you can only question the conditional statement if it is the conclusion of the argument.


The way to recognize conditional statements is by determining whether the entire statement holds true no matter what, or if it is only describing what would happen in specific instances. For example, take the following statements:


"James is the best basketball player in the league"

"James is the best basketball player in the league when he practices"


The first statement is NOT a conditional because it is describing something that is currently the case, regardless of any outside conditions that may occur. In the second statement, James is the best basketball player in a specific situation--when he practices. Therefore, it is a conditional statement.




 

How to Diagram Conditional Statements


Due to the implications of conditionality, it makes sense to diagram conditional statements to help keep track of these details. This is especially useful in situations when there are multiple conditional statements. If you don't diagram, you will be forced to hold all the details in your head at once. And believe me, the LSAT loves to trick people with the little nuances of conditional statements.


To diagram, you should use arrows. It is EXTREMELY important that you understand where the arrow points, and you will see why later in this post.


The arrow should ALWAYS point FROM the sufficient to the necessary. In other words, the arrow should be pointing TO the necessary condition.


Take the following conditional statement as an example:

"In order to vote, you must be at least 18 years old"


In this case, "at least 18 years old" is a requirement, because it must be the case. Therefore, it is the necessary condition and the rest of the statement becomes the sufficient by default. Therefore, the arrow needs to point to being at least 18 years old, like so...


Vote --> at least 18 years old





 

Identifying Conditions


Since there are important differences between the sufficient and necessary condition as discussed earlier, we must be able to quickly and accurately identify the conditions on test day. Make sure to memorize the following terms:


Sufficient Indicator

Necessary Indicator

If

Then

All

Only

Every

Only if

When/Whenever

Must

Each

Has to

Any

Unless

None

Required

Whatever immediately follows the Sufficient Indicator term will be the sufficient condition, and what immediately follows the Necessary Indicator term will be the necessary condition. Some terms like 'unless' and 'none' require a couple extra steps.


Keep in mind this is not an all-inclusive list. There are some terms that are not listed here that can be considered sufficient/necessary indicators on the LSAT. There are too many terms to list and sometimes you can have a conditional statement without any indicator terms. For this reason, it is important to understand why these are indicators.


Let's start with sufficient condition indicators. As mentioned earlier, the sufficient condition guarantees the necessary. But how do we show that something is guaranteed? We do so by showing there are no exceptions. And the way to imply there are no exceptions is to show that something is true for an entire group or entire class of things. Therefore, if you can find a term that covers an entire group, it's the sufficient condition indicator. That is why words like "every" and "when" (which is synonymous with "whenever" or "every instance") are sufficient condition indicators.


On the other hand, we mentioned that necessary conditions are requirements. As such, necessary condition indicators are simply synonymous with "requirement", or something that is needed.





 

Understanding Conditional Implications


Remember how I said the direction of the arrow is extremely important when you diagram a conditional statement? Let's go over why that's the case.


Let's use the following conditional statement...

If I'm in LA, then I'm in California


This can be diagrammed as...

LA --> California



We know this statement to be true in everyday life. In this statement, "if" signifies that LA is the sufficient condition, and California is the necessary condition. Let's experiment with each condition to see what happens in different scenarios.



  • If I am in LA, then I MUST be in California.

    • Key takeaway: If the sufficient condition occurs (being in LA), the necessary condition must occur (being in California)

  • If I am NOT in LA, then I MAY OR MAY NOT BE in California -- This is because I could be in a different city than LA that is still in California (i.e. Sacramento), or I could be in a completely different state or country.

    • Key takeaway: If the sufficient condition (being in LA) does NOT occur, we don't know what happens to the necessary condition (being in California).

  • If I am in California, then I MAY OR MAY NOT BE in LA -- This is because I could be in other cities within California aside from LA (i.e. San Francisco)

    • Key takeaway: If the necessary condition (being in California) occurs, we don't know what happens to the sufficient condition (being in LA).

  • If I am NOT in California, then I am NOT in LA

    • Key takeaway: If the necessary condition (being in California) does NOT occur, the sufficient condition does NOT occur.


These scenarios are probably the most important facts you need to understand about conditional statements. You must be able to quickly ascertain what happens in any given situation when you are given a conditional statement. It helps to first try it out on conditionals like the one exemplified above to understand the reasoning behind each scenario, but eventually you may want to make flashcards for each.


Another way to think about the implications is to understand that there are only two scenarios in which you truly know what happens to the other condition--when the sufficient condition occurs and when the necessary condition does not occur. The latter situation where the necessary condition does not occur is called the Contrapositive.


What is the point in forming the Contrapositive? The Contrapositive is just another way of saying the original conditional statement. It is the logical equivalent. Some prep companies describe this as flipping the arrow and negating both sides of the original statement. This is also technically correct and leads to the same result, but it is important to understand that negating the necessary condition of the original statement is what forms the Contrapositive.


Remember--this applies to all conditional statements. Regardless of what is given to us in the sufficient condition or necessary condition on the LSAT, the implications of each scenario still hold true.




Did you find this post helpful? Stay tuned for more insights on conditional reasoning!



Stay motivated!


Sincerely,

Cho from Impetus LSAT



If you are interested in learning more about how to study, check out more free LSAT tips or read my book on how to study.


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