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

Both phrases are incorrect. The correct form should be 'How long have you known this?' or 'How long have you known that?' The verb 'know' requires the present perfect tense when referring to a period of time that extends up to the present moment.

Last Updated: March 25, 2024

how long do you know this?

This phrase is incorrect. The verb 'know' should be in the present perfect tense when referring to a period of time extending up to the present moment.

The correct form is 'How long have you known this?' which indicates a duration of time up to the present moment.

Alternatives:

  • How long have you known this?

how long do you know that?

This phrase is incorrect. The verb 'know' should be in the present perfect tense when referring to a period of time extending up to the present moment.

The correct form is 'How long have you known that?' which indicates a duration of time up to the present moment.

Alternatives:

  • How long have you known that?

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