As an auxiliary verb: • Used with past participles of verbs to form the passive voice. • Used with present participles of verbs to form the continuous aspect. • Used with to-infinitives of verbs to express intent, obligation, appropriateness, or relative future occurrence. • Used with past participles of certain intransitive verbs to form the perfect aspect. • To tend to do, often do; marks the habitual aspect. • As a copulative verb: • To exist. • Used to declare the subject and object identical or equivalent. • Used to indicate that a predicate nominal applies to the subject. • Used to indicate that the subject has the qualities described by an adjective or prepositional phrase. • Used to indicate that the subject has the qualities described by a noun or noun phrase. • Used to link a subject to a measurement. • Used to state the age of a subject in years. • Used to indicate the time of day. • Used to indicate passage of time since the occurrence of an event. • Used to link two noun clauses: a day of the week, recurring date, month, or other specific time (on which the event of the main clause took place) and a period of time indicating how long ago that day was. • To pass or spend (time). • To take a period of time. • Used to indicate ambient conditions such as weather, light, noise or air quality. • To exist or behave in a certain way. • As an intransitive lexical verb: • To exist; to have real existence, to be alive. • To remain undisturbed in a certain state or situation. • To occupy a place. • To occur, to take place. • Elliptical form of "be here", "go to and return from" or similar, also extending to certain other senses of "go".