Auxiliary verb

Auxiliary verbs are verbs that modify the meanings of other verbs in the sentence rather than having meanings of their own. In the languages that use them, auxiliaries (or modals) are regularly irregular.

English auxiliaries are:

• Can
  • "Can" indicates ability and is superseding "may" in permission and possibility.
• Could
  • "Could" is the past tense and subjunctive of "can".
• May
  • "May" traditionally indicates possibility. As in "Mother may I?"
• Might
  • "Might" is the past tense of "may".
• Will
  • "Will" shows future time in nonpast tense.
• Would
  • "Would" is the past tense of "will" and is also used in the conditional construction. (That is, "I would go". "Would go" paraphrases the conditional mood.)
• Shall
  • "Shall" is traditionally the first person "will" and is used with threats and commands and necessities. It is falling into disuse.
• Should
  • "Should" is the past tense of "shall" and is more alive than ever.
• To Do
  • "To do" forms the emphatic forms of verbs and takes tense and person markings over from the main verb. It is also introduced into questions when there is no other auxiliary, and is brought in and negated when there is no other auxiliary.

• To Have
  • "To have" indicates pluperfective aspect and pluperfective-progressive aspect. It too takes tense and person markings over from the main verb. "To have" is also negated.
• To Be
  • "To be" forms the passive voice, progressive aspect, pluperfective-progressive aspect, helps make transitive verbs intransitive. "To be" is the most irregular of all verbs and is also negated.
• Be going to
  • "Be going to" also shows future time and is often pronounced as "gonna".
• To, while not a verb, is the auxiliary used in forming an infinitive "To" shows the infinitive of a verb. See also prepositions.

English forms yes/no questions by inverting the order of auxiliary and subject, and brings in a form of "do" if there is no auxiliary. Note that "not", "to", and "be going to" are never inverted.

"Not" negates a sentence by negating the auxiliary or the auxiliary brought in to be negated.

Some languages use "be" to form the perfect tense for some or all verbs, instead of "have", for example Esperanto (Mi estis irinta = I was having-gone = I had gone). French and German use it for verbs of motion and becoming, and (in German) for "to be" itself, as does Italian. The use of auxiliaries is one variation among Romance languages. Finnish uses ole for all verbs: "Sillä niin on Jumala maailmaa rakastanut" (Because so much is God the world loved). English uses "be" only with "go" in some senses.