half the..中half是前置限定词,属于形容词范畴,只能放在名词前使用,例如：
events that happened half a century ago半个世纪前发生的事
Kids seem to think that climbing up a slide is half the fun.孩子们好像认为大部分的乐趣在于爬上滑梯.
half of the..中half是名词,其后的of..是作为所有格来修饰名词half的,字面意思就是“...东西的一半”.当然做名词时,可以单独用,half后面可以不接of..的结构.
例如：Half of 50 is 25.50的一半是25.
An hour and a half later I was still waiting for himto arrive.一个半小时之后,我还在等着他的到来.