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

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 • 1585 views

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?

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.

Show examples from the web [+]

How long do you know this already?
Your woman, how long do you know her?
How long you know about this?
How long, do you know?
Do you know how long'?
So how long did you know Quintana?
So how long you know Rick?
New lungs work, but for how long, you know?
How long do we know eachother?
Were they married long, do you know?
So, how long did you know Bridgett?
do you know how long I wanted this?
Tell me, how long do you know the doll?
Were they married long, do you know?
How long did she know Fletcher?
Do you know how long I looked for this?!
Do you know how long the testing process takes for medical protocols like this?
Do you know how long it takes to render a 3-D image like this?
Do you know how long it'll be before you have to deal with this?
Do you know how long I've been studying for this?

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