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"how long do you know this?" vs "how long did you know?"

The correct phrase is "How long did you know?" This is the appropriate way to ask about the duration of someone's knowledge or acquaintance with something or someone. The second phrase, "How long do you know this?" is incorrect because the verb "know" should be in the past tense when referring to a duration that has already passed.

Last Updated: March 25, 2024

how long do you know this?

This phrase is incorrect in English. The verb "know" should be in the past tense when referring to a duration that has already passed.

how long did you know?

This phrase is correct and commonly used in English to inquire about the duration of someone's knowledge or acquaintance with something or someone.

This phrase is used to ask about the length of time someone has been aware of or familiar with something or someone. It is typically used in past tense to refer to a period that has already passed.

Examples:

  • How long did you know him before he moved away?
  • How long did you know about the project before it was canceled?
  • How long did you know the answer before you raised your hand?
  • How long did you know she was coming to visit?
  • How long did you know the truth before you told me?

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