定语从句和强调句不同(It is a wise father that knows his own child)

It is a wise father that knows his own child.

这是一个强调句，但由于强调的是主语，如何判断他不是定语从句呢？

同意陈才老师的解答，另补充什么时间：这是个强调句，这个习语源于古谚，但你不可以把它当作句型来模仿造句。怎么分辨是定语从句，根据国内的教法，可以如此区别。你把It is ... that... 去掉句子成分仍然完整，就是强调句。比如：It is a wise father that knows his own child. 去掉后为：A wise father knows his own child.仍然完整，所以是强调句。It is the house where she lives. 这是定语从句，由于你去掉it is...where... 后就不成句子了。