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Hi there,

I am always confused by the tense of the word know. I mean, what's the difference between know, knew, and have known? Which should be used in what conversation?

Example 1:

A, B and C together. A said something to B, and then B asked C "You knew about this?"

Why not B use know or have known?

Example 2:

A said "I always knew he looked like Mr. Potato Head."

Why not A use know?

Example 3:

A said "I knew it" or A said "I know it"

What's the difference?

Is there any rule or something when choosing between knew or know? I always mix them up in daily talk. Emotion: sad Anybody could help?
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Example 1:

A, B and C together. A said something to B, and then B asked C "You knew about this?"

Why not B use know or have known?
All are possible, depending on context. "Knew" implies that B is unhappy that he had not been informed about this thing in a timely fashion, and wants to know if C is also complicit in the "coverup."
"Have known" would suggest that C might have been sitting on the information for some period of time.
"You know" would allow that C may be just finding out about it (very recently).

Example 2:

A said "I always knew he looked like Mr. Potato Head."

Why not A use know?
Present tense with "always" would describe habitual behavior - a repeated act. "I always take a nap in the early afternoon.
To "know something" in the simple present is a state, or a condition. It's not something you keep repeating.
"I know he looks like Mr. Potato Head! You don't have to tell me!" (This is okay.)
"I knew he looked sick yesterday."
"I know (now) that he looked sick yesterday."

Example 3:

A said "I knew it" or A said "I know it"

What's the difference?
B says, "The Cougars just won the game!" A says, "I knew it!" (He had a feeling they would win.)

B says, "Your fly is unzipped!" A says, "I know it."

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Hi aleilei;

Example 1:
A, B and C are together. A said something to B, and then B asked C "You knew about this?"
Why didn't B use know or have known?

He is asking if C knew that fact before this conversation.

Conversation 1:

A: There are diamonds in this park. If you know what to look for, you can find one. A man found a big diamond just yesterday.

B: C, did you know that there were diamonds in the park? (You always have to use "did know" or "do know" when you make a question.)
C: Oh yes, I have known that for a long time. When I was here last year, Ifound a tiny diamond.
(C is saying that he learned about the diamonds some time ago, so he has known about it for a long time.)

Conversation 2:
A: There are diamonds in this park. If you know what to look for, you can find one. A man found a big diamond just yesterday.

B: C, do you know about the diamonds in the park?
C: Oh yes, I know that because I read it on the sign at the park entrance.
(C is saying that he has present knowledge about the diamonds. He could also say: "I knew that because I read the sign at the entrance" - this means that he learned it before the conversation started.)

Example 2:
A said "I always knew he looked like Mr. Potato Head."
Why doesn't A use know? (Because A is describing something he thought about in the past (Always means from a time in the past.)

Example 3:
A said "I knew it" or A said "I know it"
What's the difference?
I knew it. - This says that A learned it in the past, and still knows it now.
I know it. - This says that A knows it now, without referring to the idea that he learned it in the past.

Say know when you just want to tell someone that you have present knowledge about something. Use "know" with simple facts.

I know that the earth is round.
I know that I have three sisters.
I know that they are showing the movie "Aliens" at the theater.

Say knew when you want to tell someone that you had the knowledge sometime before the conversation, or that you had a suspicion about something that came true. Use knew if the time is past.

Mother always knew when it was going to rain - she felt it in her bones. (past)

I just knew that I was going to get an "A" on the test. I studied harder than everyone. (present time. An exclamation when you get your test paper back, but you are telling people that you were very confident of getting an "A")
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Comments  
AlpheccaStars(You always have to use "did know" or "do know" when you make a question.)

Thanks!Emotion: embarrassed The following question is when I make a question, should I use "Did you know ...?" or "Do you know ...?" What's the difference?
Students: Are you brave enough to let our tutors analyse your pronunciation?
aleileiThe following question is when I make a question, should I use "Did you know ...?" or "Do you know ...?" What's the difference?
Always use "do" when you ask about a person:
Do you know Bob Smith?

Except if the person is dead:
Did you know Michael Jackson?
Did you know your great-grandmother?

If you are asking about a past event, you can use "did" or "do":

Did (Do) you know that the Berlin wall was knocked down in 1989?

Did is asking if I was aware of it before now; do is asking if I know it right now.
Here is a good example:
Did you know that Mary is engaged to John? (I imply that I knew about it earlier, and maybe you haven't heard the news yet, so I know a secret that you don't!)

When asking for directions or information, always use "do"
Do you know the way to the train station?
Do you know where I can get some good Chinese food?
Do you know when Mary's getting married?

There are probably other differences, but I can't think of other examples right now.
aleileiExample 1:
A, B and C together. A said something to B, and then B asked C "You knew about this?"
Why not B use know or have known?
B asked C "You knew about this?" means B suspects C already learned about it earlier and that, therefore, C has known about it since he learned it, and C now knows it.

"Do you know about this?" suggests that B doesn't think that C knows. B may want C to know. "Have you known about this?" just doesn't make a lot of sense. It asks if C has continued to know it since he learned about it, which is obviously true. There is no need to ask such a question. "have known" typically goes in a question like this: "How long have you known about this?"
aleileiExample 2:
A said "I always knew he looked like Mr. Potato Head."
Why not A use know?
This is equivalent to "I have always known he looked like Mr. Potato Head". The knowing is continuous from when you learn it until now. "I always know" makes no sense. If you know something, obviously you "always" know it, so "always" is not used. If you are aware of a repeated pattern, however, you can say, "I always know when the postman delivers the mail because our dog starts to bark".

"know" is used with the present tense. You can say, "I know he looks like Mr. Potato Head".
aleileiExample 3:
A said "I knew it" or A said "I know it"
What's the difference?
"I knew it" means you had knowledge of it in the past. For example, you may be talking about your success in the past at answering some question you were asked. In some contexts it can also imply that you had suspected it to be true for some time and are now finding your suspicions confirmed.

"I know it" means you have knowledge of it now. You may be informing someone that they need not go into details explaining it to you because you are already familiar with the information at hand.

CJ