The verb "is"
When arguing about something, the verb "is" should be avoided as much as possible because of its ambiguity. "A is B" can represent: Identity: life is life. Membership to a class: a car is an object. An attribute: this apple is green. A relationship: 5 is greater than 3. A modification of a verb: John is walking. ... probably other meanings I'm forgetting now. Of course, in colloquial language "is" cannot be avoided and is not normally a problem.