Such creatures have rarely been seen alive by man .请问alive是什么成分?

Such creatures have rarely been seen alive by man .请问alive是什么成分?
为什么alive会放到seen的位置?变成such alive creatures have rareky been seen by man不是更好吗?
★★更正★★
看过下面的后置定语规律，觉得之前的问题写错了，现更正：“为什么alive会放到seen的位置？变成《《such creatures alive have rareky been seen by man》》不是更好吗？”
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以a-开头的表示状态的形容词，一般在句子中当表语成份，但作定语时须后置，类似的形容词有：alive,asleep,alike,alone.awake,aware,ashamed,adrift,ablaze,absent,afraid,available等如：
He spoke like a man afraid.他说话的时候像是很害怕似的。
Tom was the only boy awake at that tine.那时汤姆是唯一醒着的男孩。
The house ablaze is next door to mine.那着火的房子就在我家隔壁。