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 • 900 views

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.

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?

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.

Show examples from the web [+]

Your woman, how long do you know her?
How long, do you know?
Do you know how long'?
How long do you know this already?
How long you know about this?
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?
How long has the house been abandoned, do you know that?
Were they married long, do you know?
So, how long did you know Bridgett?
Tell me, how long do you know the doll?
Were they married long, do you know?
How long did she know Fletcher?
Life is long, you know? Live it up.
How do you know that?.
- How do you know that? - Emily was a redhead.
-How do you know that? -Go there all the time.
How do you know that? I'm taking Frost's advice.

Alternatives:

How long have you known that?

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