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.