# The author uses the word "immediacy" (line 39) most likely in order to express

alexjmarch on March 27, 2020

Either/or

Hi, I think there is a mistake in the either/or segment of the sufficient and necessary condition video. At 1:02-1:03, The narrator states that it is possible for both variables in an either/or situation to exist or occur. This seems wrong. Either/or means that 1 of 2 variables occurs, but not both.

Skylar on March 27, 2020

@AlexM1215, happy to help!

Though it may not seem intuitive, there is actually a difference between the phrase "either/or" and the phrase "either/or but not both." You will see this concept again in the Group Games lesson.

If we are simply told "either A or B must exist," we could have any of the following scenarios be true:
- A exists and B does not exist
- B exists and A does not exist
- A and B both exist
The only impossible scenario would be that neither A nor B exists.

Therefore, you can think about the statement "either A or B must exist" as saying "at least one (possibly both) variables must exist."

However, if the statement says "either A or B must exist, BUT NOT BOTH," then the only possible scenarios are:
- A exists and B does not exist
- B exists and A does not exist
Our impossible scenarios are:
- A and B both exist
- neither A nor B exists

You will see a similar phenomenon with the phrase "A and B do not both exist." With this, we could have any of the following scenarios:
- A does not exist and B exists
- B does not exist and A exists
- neither A nor B exist
The only impossible scenario would be that both A and B exist.

Therefore, you can think about the statement "A and B do not both exist" as "at least one of (possibly both) variables do not exist."

Does that make sense? Please let us know if you have any other questions and best of luck with your studies!