Which one of the following statements most accurately characterizes a difference between the two passages?

Matthew on January 30, 2019

Yin &Yang

I'm having a problem grasping how the logically opposite of must be true is not necessarily true. Wouldn't the opposite of must be true be that it cannot be true. I can memorize all day long, but I'm missing something fundamental about this.


Ravi on January 31, 2019


Great question. It sounds like when you're identifying the logically
opposite statement, you're putting the "not" in the wrong place. Let's
take a look.

Must be true

What's the logical opposite?

(NOT) must be true

Not must be true also means not necessarily true.

The way you're doing it, you're putting NOT in between "must" and "be"
so that must be true turns into must NOT be true. Must not be true
also means cannot be true.

The problem with the way you're doing it is that that's not how you
figure out the logical opposite. When you figure out the logically
opposite statement, you have to put NOT before the ENTIRE PHRASE that
you're looking at.

Must be true

NOT must be true = not necessarily true.

Just remember to put your NOT before the whole thing, and that should
help you keep things straight.

Does that make sense? Let us know if you have any other questions!