The verb “be” happens to be one of the most versatile and most often used words in the English language. As you say, it’s used as an auxiliary verb and can also be used as a main verb, but it’s incorrect to call it the collective word for the various forms it takes in the language. It’s a unique word by itself that also happens to be a highly irregular verb—meaning that it doesn’t obey the usual conjugation rules for regular verbs but changes into altogether new words when doing particular grammar tasks. In particular, as an intransitive verb, “be” has so many denotations or meanings and takes on different forms; as a verbal auxiliary, it has four distinct uses in the formation of the various tenses of verbs, also taking on different forms and even working with other verbal auxiliaries to evoke a specific tense and sense for a verb. You can appreciate how versatile and hardworking “be” is by going over the definitions below that I have excerpted from the
Merriam-Webster’s 11th Collegiate Dictionary.
Having clarified the nature and functions of “be,” I can now tell you that the various forms of “be” that you mentioned—“is,” “was,” “were,” “am,” “been”—are not its collective in the true sense of that word. They are just
inflections of “be,” or the changes in form that “be” undergoes to mark the case, gender, number, tense, person, mood, or voice of the sentence where it is used. As such, they are unique words in themselves, distinct from “be” and each with a specific functional role in the language.
be
intransitive verb
1 a : to equal in meaning : have the same connotation as : SYMBOLIZE <God is love> <January is the first month> <let x be 10> b : to have identity with <the first person I met was my brother> c : to constitute the same class as d : to have a specified qualification or characterization <the leaves are green> e : to belong to the class of <the fish is a trout> — used regularly in senses 1a through 1e as the copula of simple predication
2 a : to have an objective existence : have reality or actuality : LIVE <I think, therefore I am> <once upon a time there was a knight> b : to have, maintain, or occupy a place, situation, or position <the book is on the table> c : to remain unmolested, undisturbed, or uninterrupted — used only in infinitive form <let him be> d : to take place : OCCUR <the concert was last night> e : to come or go <has already been and gone> <has never been to the circus> f archaic : BELONG, BEFALL
verbal auxiliary
1 — used with the past participle of transitive verbs as a passive-voice auxiliary <the money was found> <the house is being built>
2 — used as the auxiliary of the present participle in progressive tenses expressing continuous action <he is reading> <I have been sleeping>
3 — used with the past participle of some intransitive verbs as an auxiliary forming archaic perfect tenses <Christ is risen from the dead — 1 Corinthians 15:20(Douay Version)>
4 — used with the infinitive with to to express futurity, arrangement in advance, or obligation <I am to interview him today> <she was to become famous>
