considering既然可以为连词,为什么可以跟that 从句.一个句子不是只能用一个连词吗?

considering不是连词，是介词。
就拿好奇爱楼楼的句子来说吧，
Considering that it was his fault, we shouldn't have blamed her....

that是连词，将"it was his fault"转换成名词形式，成为considering的介词宾语。介词和连词是可以连在一起使用的。

not really...considering that can be joined

eg

Considering that it was his fault, we shouldn't have blamed her....

如果跟that的时候,那么他就不是连词了,而是动名词了.
动名词是可以接从句的,表示同时发生的某种状态.
拿楼上的例子来说,Considering that it was his fault修饰we的,其中that后面的是considering的宾语.
如果没有解释清楚,请继续补充提问

温停眉

超强!

not really...considering that can be joined