2.8 - Could Be True vs. Must Be True

Next we're covering the differences between what could be true and what must be true on the LSAT.

In this lesson we will:

• Define the terms "Could Be True" and "Must Be True"
• Explain their relationship to each other and their "false" counterparts
• Visualize these relationships

Let's get started.

Defining Could Be True and Must Be True

Think about these concepts in the abstract for a moment. What does it mean when something could be true? What does it mean when something must be true?

For our purposes, could be true means possible or plausible and must be true means certain or definite.

When we're asked to identify what could be true, we're being tested on the possibilities. When we're asked about what must be true, we're being tested on the certainties.

"Must" Contains "Could"

I should note that "must" and "could" have a one-way relationship. That is, "must" contains "could" but not the other way around.

What if I told you snow was in the forecast tomorrow. You'd know there's a solid chance it could snow tomorrow. But must it? Of course not.

Now let's say tomorrow came and went, and we're left with a 2-inch blanket of powder as far as the eye can see. Must it have snowed? Yes. Could it have snowed? Also, yes.

This is to say, we pass "could" en route to "must".

Variations on Could Be True and Must Be True

Here's where the concept starts confusing some LSAT students.

It's easy for most students to understand that "could be true" means possible and "must be true" means certain.

But what happens when the LSAT trades true for false? Or when they throw in that pesky word except?

‍Let's break down these ideas one at a time.

"Must Be" = "Could Be, Except"

We already know when something "must be true", it has to be true, 100%.

But when we're asked "What could be false except...", we're looking for essentially the same thing—an exception to the thing in question possibly being false. In other words, something that can't be false and therefore must be true.

The same concept works for things that must be false.

If something must be false, we know it's impossible. It can't occur. So, when we're asked "What could be true except...", we're looking for an exception to the thing in question possibly being true—i.e. something that can't be true, that must be false.

Here's a diagram to hammer home the point:

"Must Be, Except" = Everything Else

When we talk about exceptions to what must be true or false, we're including all of the other possibilities.

If we're asked to find "What must be true, except...", we're looking for something that could be true, could be false, or that straight up must be false. Each possibility qualifies.

Here's this concept diagrammed:

Similarly, if we're asked to find "What must be false, except..." we need anything that isn't definitely false—something that could be true, could be false, or that must be true.

And here's this concept diagrammed:

Putting It All Together

Let's recap.

• "Must be" means certain. "Could be" means possible.
• En route to "must", we inevitably pass through "could".
• "Must be true" means definitely true, and is the same as saying "could be false, except".
• "Must be false" means definitely false, and is the same as could be true, except".
• Anything that doesn't have to be true qualifies when asked "What must be true, except...?"
• Anything that doesn't have to be false qualifies when asked "What must be false, except...?"

Here's a final diagram tying everything together:

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What did I miss? What about Could Be True and Must Be True still isn't clicking for you? Leave me a comment below to help me improve this course for you and future test-takers alike.

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Our next lesson's all about arguments—their anatomy and how to spot each part. See you there!