As a principal verb have is used in the sense of possess, take, experience, receive etc.

• They have a car. (possess)
• She has two daughters. (possess)
• I had a letter from my son. (receive)
• We have dinner at 9 pm. (take)
• She had an accident. (experienced)

As an auxiliary verb

Have combines with the past participle form of verbs to form the present perfect tense.

• I have completed my work.
• She has created a problem.
• I have invited my friends.
• They have received our letter.

Had combines with the past participle of verbs to form the past perfect tense.

• I had tried this before.
• They had forgotten to send the letter.

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1. What are Auxiliary verbs?