I thought

What's the difference between "I thought I knew" and " I thought I know"?

I was told that the verb following "I thougt" must be past tense.

(Goodman, hope you don't mind me using your words. I don't mean to pick on you,
just trying to learn from your posts and any other gurus' here. Maybe you could reply to this)

Thanks in advance.

Thanks YoongLiat for confirming that.
Come to think of it, it could have been just a typo. Afterall,
the difference is only one letter. I've made more severe typos.

The bottom line is, a learner (even for me) may have a hard time deciding if it's a singular or plural verb agreement, even though I thought I know!

Actually, I didn't think I was a typo either so I created this thread.
But after YL replied, it thought it could have been a typo since the difference is only one
character. Well, I guess we need more confirmation. Maybe it's matter of style. It could be
grammatically incorrect but idiomatic to native speakers. I don't know. We'll see.

 

I'm not a native speaker but I am pretty sure the version with the present tense "I though I know" sounds quite odd. You could hear something similar when "I know" is reported as direct speech, or is not really linked to "I thought":
There was this girl, you know, and... like, I thought, "I know her... I'm pretty sure I know her", you know, I had that weird feeling.

But I'm sure that's not what you meant. In non-broken speech, you need to use the past tense after verbs like thought, didn't think, felt, knew, etc. Verbs like those seem to force a backshift in tense because they are more related to your "feelings" at a certain moment in the past than the "information" you had or got.
Oh, so you are American? I thought you were Canadian! I didn't know you were from Florida.

New2grammar

What's the difference between "I thought I knew" and " I thought I know"?

I was told that the verb following "I thought" must be past tense.

Kooyeen has the answer:

you need to use the past tense after verbs like thought, didn't think, felt, knew, etc. Verbs like those seem to force a backshift in tense because they are more related to your "feelings" at a certain moment in the past than the "information" you had or got

Memorize:

I thought I knew / I thought I had to / I thought I was / I thought they were / I thought I could / I thought they would /  ...

I knew I had to / I knew I was / I knew they were / I knew I could / I knew they would / I knew they wanted / ...

I felt I knew / I felt I had to / I felt I was / I felt they were / I felt I could / I felt he would / ...

I hoped I was / I hoped they were / I hoped I could / I hoped I didn't have to ...

I believed I knew / I believed I could / I believed they were / I believed I was / ...

I didn't think ... / I didn't know ... / ... / Did you know ...?  / Did you feel ...?  / ... (same for negations and questions) 

Adding that doesn't change the basic principle here:  I thought that I knew ... 

_____________ 

And don't attempt to use present tense after thought, knew, felt, hoped, or believed -- and you'll be fine.  You'll sound just like a native speaker.

But put a present tense there (I knew they are / I thought I am / I hoped I can / ...), and you'll expose yourself immediately as a non-native!!!

CJ 

P.S.  If you make a distinct pause in speech to indicate a direct quote, these principles do not apply:

I thought, "I know how to do that.  Why are they saying I don't?"

I thought [ short pause ] I know how to ...

You absolutely cannot use the complementizer that in this case:

*I thought [ short pause ] that I know how to ...   (NO!)