"I thought you were a girl." / "I thought you are a girl."

[xiaoen]

Hi,
Let's suppose that I chat to a girl on the Internet. Later I realize that she is not really a girl but a boy and he was chatting to me with a fake female name. Now I want to tell him this sentence:

"I thought you were a girl."
"I thought you are a girl."

Are both acceptable? What's the difference?

 

[Matthew Wai]

'You are a girl' is not what the speaker thinks in the present, so the present tense 'are' is not suitable.

 

[Raymott]

That's irrelevant Matthew. She reporting what she thought (past tense).

 

[emsr2d2]

If you're talking in real time, you might say "I thought you were a girl. Now I think you are a boy" or "Now I know you are a boy". I imagine the next word would be "Goodbye"!