taken together 为什么要用taken?

taken together 是 take together（将...联系在一起 /把 …合并考虑/把…算在内）的过去分词短语,可以用来作状语,它的逻辑主语就是句子的主语,与该主语是动宾关系,其作用相当于一个状语从句,即“如果/要是‘充当主语的名词’被考虑在内”.如：
 

Taken together,these volumes provide a range of topics.这些卷书总合在一起提供了一套专题.【= If these volumes are taken together】

 Taken together, the chill and the vapour told a poor tale of the island.寒气和这白色的雾霭混杂在一起,表明这座小岛环境恶劣.【= when the chill and the vapour were taken together】 

Taken together,it was only meant for a joke. 充其量那只是个笑话.【= if it was taken together】