It is clear that none of the volleyball players at yesterday's office beach party came to work today since everyone w...

Kenny September 7, 2015

Sufficient and necessary terminology

The video explanation said that "everyone", "no one" and "none" are sufficient and necessary terms, however looking at the old videos, I can't determine whether they introduce a sufficient or necessary.

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Naz September 9, 2015

Remember that the most important thing with Sufficient & Necessary is not to blindly follow rules and to take everything in context. With that said, more often then not, the words you indicated introduce sufficient conditions. However it gets trickier with the "none" and "no one" due to the negation.

Let's look at some examples:

(1) Everyone of A is B.

So this means: If A, then B.

A ==> B
not B ==> not A

(2) No one that has A will have B.

So this means: If A, then not B.

A ==> not B
B ==> not A

(3) None of A is B.

So this means: If A, then not B.

A ==> not B
B ==> not A

Hope that helps! Please let us know if you have any other questions.