i didn't know they would go to Japan 为什么是they would

问题描述:

i didn't know they would go to Japan
为什么是they would

因为是didn't,时态是过去时,know后面省略了一个that,后面是一句完整的句子,时态也是过去时,所以用would

would在这里作为will的过去时.
这句话的意思是:我不知道他们要去日本.
在这句话中,他们要去日本是已经决定好的事了.所以用过去时.