helping verb

A helping verb, sometimes called an “auxiliary verb”, is another word added to the main verb to indicate changes in tense. For example,

 I have read.  “have” is used to make the perfect tense
 I will be writing you a letter. “will” is used to make the future tense
 I certainly did see a musk ox.  “did” is used to make the emphatic tense

In the last sentence, “certainly” is not a helping verb but an adverb.