Be not (is not /are not)
The negated verb not to be and its conjugated forms are used for negating a concept or giving a complement concept.
Those examples show how to use the negated verb not to be to negate a concept or to give a concept complement to it.
Example: Everything in the world is an adult-thing or a young-thing. The concepts are complement.
Something is a young-thing if-and-only-if-it is not an adult-thing.
Example: The classes of young-thing and adult-thing are disjoint. However, there might exist a thing that is neither of them.
Every-single-thing that is a young-thing is not an adult-thing.
Every young-thing is not an adult-thing.