Auxiliary verb

An auxiliary verb is a helping verb placed in front of a main verb to build a tense, a voice, a question or a negative — the 'had' in 'had waited', the 'was' in 'was taken'.

The primary auxiliaries are be, have and do; the modal auxiliaries are can, could, may, might, must, shall, should, will and would. Each one adds a layer of tense, possibility or obligation to the verb that follows.

• She had waited. — tense.
• The file was taken. — passive voice.
• Did she call? — question.
• She might have been waiting. — three auxiliaries and a participle.

That last one is the pattern to watch. Every auxiliary you add puts more distance between the reader and the action, and in narrative prose that distance reads as hedging. She might have been waiting is four words further from the scene than She waited, and it is the same effect described under filter words: the event reaches the reader through a layer of apparatus.

Two useful habits. Cut had down to one use when entering a flashback, then move to the simple past, because sustained past perfect is heavy. And treat any modal in a line of narration as a question worth asking — would often go is usually just went.

Do not confuse an auxiliary with a linking verb: the auxiliary always has another verb after it.