From UNL Wiki
The verb "to be" may be used, in English:
- as an intransitive verb, to be represented by the corresponding UW;
- as a linking verb (copula), to be represented by a relation; and
- as an auxiliary verb, to be represented by attributes.
- "To be" as an intransitive verb (=UW)
- To exist in actuality; have life or reality: I think, therefore I am.
- To occupy a specified position: The food is on the table.
- To remain in a certain state or situation undisturbed, untouched, or unmolested: Let the children be.
- To take place; occur: The test was yesterday.
- To go or come: Have you ever been to Italy? Have you been home recently.
- "To be" as a linking verb (= relation)
- To equal in identity: "To be a Christian was to be a Roman" (James Bryce).
- To have a specified significance: A is excellent, C is passing. Let n be the unknown quantity.
- To belong to a specified class or group: The human being is a primate.
- To have or show a specified quality or characteristic: She is witty. All humans are mortal.
- To seem to consist or be made of: The yard is all snow. He is all bluff and no bite.
- "To be" as an auxiliary verb (= attribute)
- Used with the past participle of a transitive verb to form the passive voice: The mayoral election is held annually.
- Used with the present participle of a verb to express a continuing action: We are working to improve housing conditions.
- Used with the infinitive of a verb to express intention, obligation, or future action: She was to call before she left. You are to make the necessary changes.
- Archaic Used with the past participle of certain intransitive verbs to form the perfect tense: "Where be those roses gone which sweetened so our eyes?" (Philip Sidney).
- The intransitive verb, but not the linking verb, may be replaced by an equivalent verb without changes in the meaning or in the structure
- The food is on the table = The food is placed on the table
- The test was yesterday = The test took place yesterday
- Have you ever been to Italy? = Have you ever gone to Italy?
- A is excellent = ?A means/is equal to excellent (= different meaning)
- The human being is a primate = ?The human being belongs to the class of primates (=structural change)