Parallel Reasoning Questions
These questions present you with an argument, and your job is to select another argument that follows the exact same logical structure.
Parallel reasoning questions can be very tricky, and there seems to often be one unusually hard one towards the end of each section. However, this guide will give you easy steps that should get you to the right answer every time.
In order to find an argument that has a matching logical structure to the stimulus, you’d have to first figure out what the logical structure of the stimulus is. This is why I recommend boiling the paragraph down into its logical skeleton as you read it. Then, all you have to do is find the answer choice that has the same logical skeleton.
Here’s what I mean by logical skeleton. Let’s say I gave you a question like this:
Whenever John skips breakfast, he’s extra hungry at lunchtime. If John is extra hungry at lunchtime, he eats a bagel for lunch. Therefore, on days that John skips breakfast, he eats a bagel for lunch.
Which one of the following most closely parallels the above argument in its reasoning?
If you had to boil this down into its logical skeleton that got rid of all of the specifics about John and breakfast and bagels, it would look like this:
If X, then Y.
If Y, then Z.
Therefore, if X, then Z.
In this case, X is John skipping breakfast, Y is John being extra hungry at lunchtime, and Z is John eating a bagel for lunch. We use arbitrary letters that have nothing to do with the specifics of the argument so that we can test out other arguments against this skeleton to see whether they match.
Here’s an example that would have to be the right answer:
If Shauna goes biking on Sunday afternoon, she gets a good night of sleep that night. Whenever Shauna gets a good night of sleep on Sunday, she has a fruitful week. Therefore, whenever Shauna goes biking on Sunday afternoon, she has a fruitful week.
The trick is matching everything in the answer choice with the skeleton you created. In this case, going biking on Sunday afternoon is X, getting a good night of sleep is Y, and having a fruitful week is Z.
It’s important to note that while the correct answer must parallel the stimulus in its logical skeleton, it need not be parallel in its sequence. In other words, the following arguments would all be considered parallel:
If X, then Y.
If Y, then Z.
Therefore, if X, then Z.
If Y, then Z.
If X, then Y.
Therefore, if X, then Z.
If X, then Z,
since if X, then Y,
and if Y, then Z.
If Y, then Z.
Therefore, if X, then Z,
since if X, then Y.
These are all the same logical skeleton, in that they use they same two premises to get to the same conclusion, albeit in different sequences. Here are some actual arguments that would all be considered parallel to this structure, despite varying sequences – see if you can identify X, Y, and Z in each one.
Anyone who eats carrots regularly has great skin. Hence, eating carrots regularly gives a person the ability to become a model, since anyone who has great skin can become a model.
Using the MasterLSAT method will ensure that your score improves. After all, efficient study methods guarantee score improvement, and using the MasterLSAT method will cause you to use efficient study methods.
Having a comfortable life gives a person a pleasant demeanor. Going on vacation twice a year ensures a comfortable life, so going on vacation twice a year gives a person a pleasant demeanor.
In the first example:
X = eating carrots regularly
Y = having great skin
Z = ability to become a model
In the second example:
X = using the MasterLSAT method
Y = using efficient study methods
Z = score improvement
In the third example:
X = going on vacation twice a year
Y = having a comfortable life
Z = having a pleasant demeanor
Get good at finding logical skeletons and matching up each of the elements into a different argument.
Here’s an example of a different logical skeleton:
Every resident of Canada is very polite. Hence, Cathy, who is a Canadian resident, must be very polite.
This skeleton would look like this:
Every X is Y.
Therefore, since this one person/thing is X, it is Y.
And here are some arguments that would be considered parallel:
This tomato must be healthy, since it’s a vegetable, and all vegetables are healthy.
Every student at Columbia Law School got a high LSAT score. Consequently, Jessie must have gotten a high LSAT score, since she is a student there.
My iMac, which is an Apple product, must be good, since all Apple products are good.
This structure of introducing a general rule and then applying it to a specific case comes up often on these questions (i.e. this general rule pertains to ALL Canadians/vegetables/Columbia students/Apple products, therefore, it must apply to this ONE instance).
So far, the arguments we’ve been dealing with have been inherently good arguments, without any logical flaws. However, parallel reasoning questions come in two flavors: good reasoning and flawed reasoning.
In other words, sometimes you’ll be presented with a flawed argument, and you’ll have to find another argument with parallel flawed reasoning.
These are generally trickier. Sometimes an argument just seems bad and you can’t figure out why – however, here you have to find an argument that’s bad in the exact same way as the stimulus argument.
Let’s take a look at an actual question from June 2007. This argument uses a general rule to make a conclusion about a specific case, like the examples I just gave you, except this time it’s a flawed argument.
Let’s map out the logical skeleton:
All of X are high on a particular scale.
All of Y are low on that same scale.
This thing is part X and part Y, which means it’s moderate on the scale.
This is the most general way possible to map this argument out. X is Labrador retrievers, Y is Saint Bernards, the scale represents how much they bark, and the instance (“this thing”) is Rosa’s dogs. Labs bark a lot, Saint Bernards don’t bark much, so the conclusion is that any mix of those two dogs must be halfway in between on the barking scale.
This is not necessarily a valid conclusion. Just because two things are on opposite ends of a spectrum, doesn’t mean that if I mix them together the result will be on the middle of the spectrum.
At any rate, our job isn’t to prove why this argument is flawed. All we need to do is find another argument with the same (flawed) structure.
(D) is a tricky answer that many people picked, since at face value it is very similar. Transcriptionists would be X, engineers would be Y, and Bob would be the instance of the two of them mixing. However, recall exactly what the skeleton is – to be the right answer the argument would have to conclude that Bob partly knows shorthand and partly knows calculus, but it doesn’t – it says he knows both of them. The original argument put Rosa’s dogs halfway in between being frequent barkers and rare barkers – it didn’t say they were both frequent barkers AND rare barkers. This would be impossible since these two things are mutually exclusive, as they’re on either ends of a scale of the same measure: barking. (This marks a difference between the stimulus and (D), since knowing calculus and knowing shorthand are not mutually exclusive – they’re not on opposite ends of a scale, and therefore a person could be both of them.)
In fact, (D) is a fairly solid argument – if Bob was both an transcriptionist and an engineer, it would stand to reason that he would have to know both calculus and shorthand. The fact that this argument is not flawed is also a giveaway that it can’t be the right answer. The same would be true if you found a flawed argument in the answer choices of a parallel good argument question. (Note that with parallel reasoning questions, if it doesn’t say “flawed” in the question, you know you’re looking at a good argument.)
Back to the other answer choices – (B) looks like it matches our logical skeleton perfectly. X is type A chemicals, Y is type B chemicals, this household cleaner is the instance of part X and part Y, and this time, there is a scale on which X and Y are at opposite ends – the scale of toxicity. X is very toxic and Y is not toxic, so the argument concludes that the mix of the two must be moderately toxic. X and Y are measured on the same scale, and the mix is said to be halfway in between on that scale.
(Answer choice (B) may also help to demonstrate why this logic was flawed in the first place. Mixing a very toxic substance with a nontoxic substance doesn’t necessarily produce a moderately toxic substance – it may still produce a very toxic substance!)
Sometimes, a trick that can help in finding the right answer is to pause after reading part of an answer choice and think to yourself, “how would this answer choice have to continue in order to be the right answer?” Then, keep reading and see whether it matches or not. This can be a good way to keep your bearings and avoid getting lost in tricky answer choices.
Let’s look at one more from the same test, also dealing with a flawed argument:
The conclusion is stated in the first line, and the support is what follows (after the word “because”). Essentially, to simplify this argument (which is always the right thing to do if possible), this argument concludes that we should accept the proposal since some people who have an ulterior motive think that we shouldn’t accept the proposal.
In other words, here’s our skeleton:
Some people with an ulterior motive think we should take a certain course of action.
Therefore, we should not take that course of action.
(A) begins by recommending a course of action. It says we should “attempt to safeguard works of art” in the first line. What would it have to say after the first sentence in order to match our skeleton?
It would have to continue by saying that the reason we should do this is because there is a group of people who thinks we shouldn’t safeguard these works of art, but that they have some kind of ulterior motive. Does it say this? No. There are no people identified here who disagree with this recommendation. (It says people may disagree on whether they have cultural significance, but that’s not the same thing as disagreeing on whether to safeguard them. Also, no ulterior motives are noted.) Thus, (A) is wrong.
(B) is a pretty solid argument, and also has no naysayers or ulterior motives. Therefore, it must be wrong.
(C) begins by recommending a course of action: namely, that you should have your hair cut once a month or less. Pause – how would it have to continue in order to match our skeleton?
It would have to go on by citing as evidence that there is a group of people who disagree and recommend haircuts more than once a month, but that these people have some kind of ulterior motive. Does it say this? Yes! Beauticians recommend more than one haircut per month (two per month), and they have an ulterior motive (making more money). Therefore, this must be the correct answer.
(D) says we should endorse a plan because a group of people would be in favor of that plan, not because they’re against it and have an ulterior motive. Therefore, it’s incorrect.
(E) also never cites a group of people opposed to a course of action for any motive whatsoever.
- Whether a good or flawed argument, start these questions by identifying the logical skeleton of the stimulus
- Simply find the answer choice that matches that skeleton
- Sequence of statements is unimportant; logical structure is what matters
- It can help to pause after reading part of an answer and determine how it would have to continue in order to be the right answer
For full clarity on very tough logical reasoning questions, check out my comprehensive LSAT course.
Oh, and if you haven’t already, download your Free MasterLSAT Study Guide, which will tell you exactly what you need to do to reach a 99th-percentile score on the LSAT.