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3 Ways to Weaken An Argument

Understanding how to weaken an argument can be considered the foundation for the vast majority of Logical Reasoning (LR) questions. For example, not only would this of course help with Weaken questions, but you may have heard that the correct answer choice for a Necessary Assumption is one that would weaken the argument if it were negated. Similarly, Flaw questions require an understanding of potential claims that would weaken the argument. So, mastering this concept will pay huge dividends, as the skills you acquire have ripple effects into many question types. In this post, we will discuss the 3 ways to effectively attack an argument.


  1. Attack the Assumption

This is the most common way the LSAT tests your ability to weaken an argument. If you are often unable to see why a correct answer is correct, you may have issues within this skill set. After reading an argument for an assumption-based question (Weaken/Strengthen, Necessary Assumption, Sufficient Assumption, Flaw), you should always ask yourself "Even if the premise(s) are true, does the conclusion have to be true?" or "What additional statement would make the conclusion and premise less related to each other?"

For example, suppose we had the following argument...

Henry donated a lot of money to charity. Therefore, he is a good person.

In this case, the premise (aka support) for the argument is that Henry donated a lot of money to charity. The conclusion (signified by "therefore") is that he is a good person. But does the conclusion have to be true even if we accept that he donated money to charity? Not really. Let's think of a few statements that would make the conclusion less likely even if the premise was true.

-Henry only donated money for a negative ulterior purpose

-Many people who donate money are terrible

If we knew either of these statements to be true in addition to the premise, it would directly attack the relationship between the premise and conclusion, and in the process would make the conclusion less likely to be true. Notice how these statements make it clear that donating money (the premise) does not necessarily guarantee someone being a good person (the conclusion), rather than attacking a single statement in isolation.


2. Directly Attack the Conclusion

Let's take the same exact argument. Here it is again for reference:

Henry donated a lot of money to charity. Therefore, he is a good person.

Another way to attack this argument is by directly questioning the conclusion without consideration of the premise. Here are a few examples:

-Henry is a murderer

-Henry is selfish

Notice how these statements don't mention anything about donating money (the premise), yet they bring up outside information that would make the conclusion less true or flat out false. For example, if Henry is a murderer, I bet a lot of people would start to question whether he is truly a good person.

For this reason, understanding the conclusion is extremely important because the conclusion is often nuanced and the correct answer will often play on those little details.


3. Directly Attack the Premise

This is the least common way to weaken an argument on the LSAT. For this reason, a lot of prep companies say that you should always assume the premises are true, which can be misleading. I want to clear the air and say that there are definitely situations where you can directly attack a premise. In fact, sometimes the question stem will explicitly ask you to. Take for example the question below from PT60 Section 2 #6:

“Which one of the following, as potential challenges, most seriously calls into question evidence offered in support of the conclusion above?”

This question is asking you to weaken the evidence, which is the premise. In situations like this, as you may have guessed, you should directly undermine the premise.

Going back to the argument about Henry being a good person, remember that the premise is “he donated a lot of money to charity”. For this type of statement, I simply need to make it less likely this happened. This could be something as simple as directly contradicting the statement.

It's important to note that this list is ordered not only in order of frequency, but also by the order of the strength in which it attacks the validity of the argument. For this reason, if the question asks you to weaken the argument, you should select the answer that weakens the assumption over the answer that contradicts a premise. It is also worth reading the question very carefully. Don't just be satisfied with understanding what question type you are dealing with--look into whether it is asking you to strengthen or weaken the premise, conclusion, or the argument as a whole, because there is a difference!

Stay motivated!


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