The negated verb to be and its conjugated forms are used for concept inclusion or concept equivalence. With that verb a hierarchy of concepts is constructed or an individual is placed in the hierarchy of concept (by saying what concepts the individual actually is). Concepts and individuals are defined when their names are used in at least one sentence.
The verb to be combined with the word by is used to create a role inversion. It is conceptually equivalent to passive voice.
Those examples show how to use the verb to be to create a hierarchy of concepts and individuals and make role inversion.
Example: Individuals are named and placed in the hierarchy of concepts.
Sophie is a giraffe.
Leo is a lion.
Example: A simple hierarchy of concepts. Lion and giraffe are inclusive of the concept of an animal.
Every giraffe is an animal.
Every lion is an animal.
Example: A simple hierarchy of concepts. Concepts of a young male man and a boy are equivalent.
Something is a boy if-and-only-if-it is a young-male-man.
Example: A more complex hierarchy of concepts. The concept of a young male man is an intersection of concepts of a young thing, a male thing and a person.
Something is a young-male-man if-and-only-if-it is a young-thing that is a male-thing and is a person.
Example: Role inversion. The last two sentences are equivalent.
Every child is loved by parent.
Mary is loved by Tom.
Tom loves Mary.