could have done 的意思

都对,这需要语境分析.
意思1：过去可能做过某事
I can't imagine how he could have thought of doing such a thing.
我不能想象他怎么会想到做这样的事.
这里的could表示对可能性的一种推测.
意思2：本来可以做某事(而实际上没做)
But for your help,I could have fed the fishes.
若不是你搭救,我恐怕已经葬身鱼腹了.
第二种意思更常见