verb helpers

[Celeste Duncan]

What do you call words like "to" when used with a verb, i.e. "to play", or "have" when used with a verb, i.e. "have played"? I'd like to know the grammatical term. Thanks.

[Tdol]

Have is an auxiliary verb
To is no so simple- some say it is a preposition, others call it a particle and others call it an infinitive marker.