分析：I didn’t know you are

问题描述

经常看到I didn’t know you were here. 这句话（宾语从句中的were用了一般过去时），“我不知道你在这儿”，按理说，其实“你就在这儿”，只是我原来不知道而已。所以you were here为什么不用一般现在时的you are here呢？

老师答疑

张老师：

▲这里一般只能用were，不能用are: I did not know you werehere. 因为这是在描述过去的事情，过去怎么能预知现在呢？如果你非要搞穿越，也未尝不可，正确的说法是这样的：I did not know you would be here.
▲那么如果你非要表示见到对方此时的身处状态，你要这样说：I am surprised/ glad to know you are here. (because I did not know, priorto meeting you, that you were here). 你同样也不能说：I do not know you are here. 因为这样不是在睁眼说瞎话嘛。

罗老师：

当因为在宾语从句里面，主句和从句时态必须保持一致，主句用的是一般过去时，那么从句也要改成相应的过去时，除非从句讲述的是一个客观真理，那就可以用一般现在时，比如：Our teacher told us the sun rises from the east.