What is the difference between I had had and I have had?

The difference between "I had had" and "I have had" lies in the tense and the context in which they are used.

Present Perfect Tense: I have had

• This tense is formed using the auxiliary verb "have" or "has" followed by the past participle of the main verb, in this case, "had."
• It is used to describe an action that started in the past and continues up to the present, or an action that occurred at an unspecified time in the past.
• Examples:
  • "I have had a fever since Monday." (The fever started in the past and is still ongoing.)
  • "I have had a dog before." (The action of having a dog happened at some point in the past, but the exact time is not specified)135.

Past Perfect Tense: I had had

• This tense is formed using the auxiliary verb "had" followed by the past participle of the main verb, in this case, "had."
• It is used to describe an action that occurred before another action in the past.
• Examples:
  • "I had had two drinks when my friend finally walked into the bar." (Having two drinks happened before the friend walked in.)
  • "I had had three girlfriends before I met the woman who became my wife." (Having three girlfriends happened before meeting the wife)123.

Key Differences

• Time Frame: "I have had" refers to an action that started in the past and may still be ongoing or has an undefined timeline, while "I had had" refers to an action that was completed before another action in the past.
• Context: "I have had" is used in the present perfect tense to connect past actions to the present, whereas "I had had" is used in the past perfect tense to show the sequence of past events235.

In summary, the choice between "I have had" and "I had had" depends on whether you are describing an ongoing or past action with no specific end time, or an action that occurred before another past action.