Must Be True vs. Most Strongly Supported LSAT Questions

Update: Practice makes perfect. You can find lists of Most Strongly Supported and Must Be True questions here: http://lsathacks.com/guide/logical-reasoning/questions-by-type/

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People often confuse LSAT “Must be True” questions and “Most Strongly Supported” questions. Some companies even teach that they are the same thing.

The questions are pretty similar. But they are not the same, and knowing the difference can you solve some of the tough questions.

First, what they have in common:

  • Both types are generally not arguments. They just state facts, and there is no conclusion.
  • Both types allow you to combine statements to make deductions.
  • For both types, the correct answer will be a logical deduction that follows from combining the premises.

So what the heck is the difference? It’s all in the strength of the deduction.

What Makes A “Must Be True” Answer Correct

Deductions for “Must Be True” questions will be 100% valid. Rock solid. There’s absolutely no room for argument. The deductions have to be true.

Whereas for “Most Strongly Supported” questions, there will be some wiggle room.

A lot of people want to argue with LSAT questions. They think that, from a certain perspective, the answers can be debated.

Those people are wrong. I tried arguing with the LSAC once. I sent them a list of my objections to the question. They sent me back about 20 paragraphs of careful explanation that convinced me, beyond a shadow of a doubt, that I was wrong. The question was right.

For a “Must be True” question, if you accept that the premises are true, then you must also accept that the answer is true.

So if I tell you that all cows have wings, and everything with wings runs on gasoline, then you must believe that cows have wings and run on gasoline (assuming you were silly enough to believe me).

What Makes A Most Strongly Supported Answer Correct

Most Strongly Supported questions are special because they allow for some level of objection. Suppose I said:

“The sun has risen every day in recorded human history. Things that have always been true in the past tend to stay true in the future.”

It’s pretty strongly supported that the sun will rise tomorrow, based on what I said. But it is not 100% certain. I could think up a million and one reasons why the sun won’t rise. I’ll almost certainly be wrong, but the point is that we have no proof that the sun will rise.

Now, if I told you that:

“The sun will rise every day. Tomorrow is a day.”

Then it’s 100% certain that the sun will rise tomorrow.

Clear as mud? Let’s look at a couple of sample questions so you can see this in context.

“Must Be True” Example

I’d like to thank my student Ola for finding me a few questions to work with for this post. Here’s a Must be True LSAT question from section II of LSAT 43. It’s question 22. I can’t print it here because of copyright, but you should go find a copy and try it yourself before reading this explanation. Here’s the link to test 43 on Amazon.

This question gives us a bunch of statements about parrots. We can’t conclude much. Here’s what we know:

  • All parrots can learn to speak, a bit.
  • Some parrots are more or less sweet than others.
  • Some parrots are Australian.
  • Some parrots have sweet dispositions (The australian ones)
  • Almost any (+90%) of parrots will like you if you hand feed it from a young age.

“Some” statements are practically useless, if that’s all you have. No, wait: they are useless if that’s all you have. Suppose I said:

“Some people are Mike, some people are Jenny, some people are Doug, some people are Romanian, some people are Elvis, some people are Bob, some people are Tina.”

Is there any overlap between those two groups? I have no idea, and neither do you. So stop trying to combine “some” statements. Bob is not necessarily Tina, though he might be if he likes wearing dresses.

Likewise, maybe some Australian parrots have been hand fed from birth, or maybe none of them are. We have no idea. None.

So let’s focus on what we do know.

We Can Combine “All” and “Some” Statements

Suppose I say that “all dogs can bark”. And I tell you “some dogs are brown, some dogs are black, and some are Dalmatians”. We can combine these statements to say:

  • All Brown dogs can bark.
  • All Black dogs can bark.
  • Dalmatians can bark.

This is true because every dog can bark. If something is a dog, it barks. Dalmatians are dogs, so they bark.

Notice that I didn’t include the word “all” with Dalmatians. It turns out that the phrases “All Dalmatians can bark” and “Dalmatians can bark” are 100% the same. If someone says “Did you ever notice that men/women are…” they’re making a claim about all men/women. That’s why those claims are so dicey!

Combining the “All” and “Some” Statements About Parrots

Anyway, back to parrots. All parrots can speak. That means that any type of parrot can speak, including the types mentioned in the stimulus, such as sweet tempered parrots. So we can say that :

  • Australian parrots can speak.
  • Sweet tempered parrots can speak.
  • Hand fed parrots can speak.
  • Martian parrots can speak.

Ok, I made the last one up, but we do know it’s true, assuming there is such a thing as a Martian parrot. Every parrot can speak, because all parrots can speak.

I made these deductions before looking at the answers. I saw nothing could be combined, except for the “all” statement + the “some” statements, so I knew the answer would be one of those combinations.

Crucially, I was looking for that kind of deduction because this is a “Must be True” question. So I knew there was a rock-solid deduction I could make, before looking at the answers.

Most Strongly Supported Example

Ok, now for a “Most Strongly Supported” LSAT question. Take a look at section I of LSAT 35, question 19. If you don’t have LSAT 35, you can find it in the LSAC’s “The Next Ten Actual Official LSATs” (it’s essential when preparing for the LSAT).

Basically, house pets often get a disease when they eat a certain legume. Scientists have tried to give rats this disease, but they’ve failed.

The right answer, C, is fairly well supported: some species (rats) are less vulnerable to the disease.

But it is not a rock-solid conclusion. There could be other reasons that rats don’t get sick. The rats live in labs, while pets live in houses. Maybe some factor in houses makes pets vulnerable. Maybe something about labs makes animals immune. Maybe scientists are really bad at infecting rats, and they would have also failed to infect pets. Maybe…I could go on forever (really).

So I would not bet my life that rats are actually more likely to get the disease. But it does seem pretty well supported, so I chose C.

I deliberately chose a most strongly supported question that had a weak answer. Most “Most Strongly Supported” questions have stronger answers than this. In a lot of cases, I suspect the LSAT chose the MSS type just to avoid lawsuits from people who say “but what if X, then wouldn’t I be right?”.

But there really is a difference between the two types. With MSS questions, you can think of a way to argue against the answer (and that’s fine). With “Must be True” LSAT questions, there is no way to challenge the answer (successfully).

Did that help clear up the difference between “Must Be True” and “Most Strongly Supported” LSAT questions? Let me know in the comments.

And if you’re looking for a way to find answers for LSAT questions by question type, check out the explanations I wrote. I’ve identified the type of every LR question.

 

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