About this video
This LSAT-style lesson works through a strengthen question. A study finds people who exercised were less likely to die, and the arguer concludes exercise increases life span. The lesson identifies the gap, a correlation treated as causation, and tests each answer choice for whether it closes that gap, weakens it, or does nothing.
You'll be able to
- identify the conclusion and support in a study-based argument
- name the gap between correlation and causation in an argument
- tell a strengthener from a weakener by how it affects the link between evidence and conclusion
Key words
- Correlation
- Two things that occur together, which does not by itself show one causes the other.
- Strengthen question
- An LSAT question type asking for the answer that makes the conclusion more likely to follow from the support.
- Weakener
- Information that makes the conclusion less likely, such as a rival explanation.
- Random assignment
- Assigning subjects to groups by chance, which makes groups more comparable.
Transcript
- [Instructor] This question asks us which one of the following, if true, most strengthens the argument? So we're looking at a strengthen question. That means that the answer will help the argument. In other words, it will make the conclusion more likely to follow from the given support, if we assume the answer to be true.
The four wrong choices will either weaken the argument or do nothing to the argument if we assume them to be true. Pause your video now if you'd like to try this question on your own. Otherwise let's move on to the explanation. Okay, let's read the stimulus. And for strengthen questions, it helps to read actively for the conclusion and the support since the connection between those two parts is what we'll be looking to strengthen.
The passage reads, a recently completed study of several hundred subjects, all of approximately the same age, showed that those who exercised regularly during the study were much less likely to die during the study. This indicates that exercise can actually increase one's life span.
Okay, is the first sentence our support or our conclusion? It's pretty safe for us to identify it as support since it involves a study. A study is just something that took place and gave certain results. And here, those results are that people who exercise regularly during the study were much less likely to die during the study.
Now, it's the interpretation of the study that often lends itself to subjectivity. And that's what we have in the second sentence with the really good signal word, indicates. The arguer is interpreting the study's result to mean that exercise can increase one's life span.
So we can mark that as our conclusion. Okay, for strengthen questions, it's usually the case that there are lots of different specific ways to strengthen the argument. And all of those ways are completely legitimate. So a specific prediction isn't necessary or even usually recommended.
Sometimes though, you might see a familiar pattern on test day, like a certain structure that you've seen a lot of in your practice. And here we see a study. When you see a study in logical reasoning, it can be a good idea to examine the potential holes in the study.
We do learn that the subjects here are approximately the same age, so that gives us one point of fairness about the study. However, we're only given a correlation and that correlation is that the people who exercised regularly were the same people who were the least likely to die.
Then what happens is we shift to causation in the conclusion. The arguer believes that one of the correlated attributes causes the other. So it's possible that a strengthener will adjust this gap and bridge it, so that the causation is more likely to be true based on the correlation that the study shows.
So to rephrase our task, we're looking for something that makes it more likely that the study is connected to real life. Great. Now that we know what we're trying to accomplish, let's evaluate the choices. A, the subjects who did not exercise regularly during the study tended to have diets that were more unhealthy.
This information actually weakens the argument. It's bringing up something else that could've caused the difference in death rates, like it's possible that it wasn't more exercise that helped people die less, but rather it was healthier diets. So choice A presents an alternative cause and that weakens the causal relationship that the arguer believes to exist.
B, the subjects who did not exercise regularly during the study tended to blame their lack of exercise on a lack of time. This information doesn't affect the argument at all. We aren't interested in what the subjects blame for their lack of exercise, we're interested in whether their lack of exercise affected their likelihood of death.
It doesn't matter that the subjects claim to not have enough time. C, a large number of the deaths recorded were attributable to preexisting conditions or illnesses. This is a lot like choice A because it weakens the argument by giving a different reason that people could have died during the study.
Maybe it wasn't lack of exercise that did it, but rather, maybe the people who didn't exercise regularly were already unhealthier than the people who did exercise regularly, for example. So this is a weakener. D, whether or not a given subject was to exercise during the study was determined by the researchers on a random basis.
This is our strengthener. This choice directly strengthens the connection of the study to the conclusion because it removes the possibility that people who didn't exercise did so for specific health-related reasons. In other words, if the researchers randomly selected who exercised and who didn't, then that random sampling makes the study more representative.
If a choice removes a potential weakener, like this choice does, then the overall effect is that it strengthens the argument because it takes away one possibility that would have hurt the argument, if it were true. For the record, choice E states a person who exercises regularly is probably doing so out of concern for his or her own health.
And this doesn't strengthen the argument. A person's motivations don't affect this argument because people could have very different motivations for exercising, but the fact remains that they exercise. And we need to know whether that exercise, whatever the motivation for it is, increases one's life span.
So to recap, for strengthen questions, you're finding the choice that helps the link between the evidence and the conclusion. It really helps to separate the evidence and the conclusion by seeing the evidence as information that we're given and then seeing the conclusion as an opinion that the arguer makes based on that information.
Well, in a strengthen question, we want to bring the two pieces closer together. We want to make it more likely for the conclusion to happen based on the evidence that was provided. It can also help to pretend that you're adding each choice to the argument and seeing which way the argument moves in quality.
Does it get better? Does it get worse? Does it stay the same? Look for any gaps in the argument, like where the evidence is addressing one thing and the conclusion addresses a different thing, and then look for a choice that helps close that gap. Or sometimes you can also strengthen an argument by removing a potential weakener, like we did in this question.
Keep a good grasp on the structure of the argument and what you're being asked to accomplish.
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