could have done 表示过去能够做而实际未做。意为“本来能够做到,而实际没做”，有惋惜、遗憾之意。或用来提出婉转的批评。

could have done 表示过去能够做而实际未做时，仅用于肯定句。

有惋惜、遗憾之意，或表委婉批评。

In those circumstances we could have done better.

在那样的情况下，我们本来可以做得更好。（但实际没有做得更好）

You could have done better, but you didn’t try your best.

你本可以做得更好，但是你没有尽力而为。

We could have finished the task, but it was always raining.

我们本可以完成任务，但是一直下着雨。

You could have given it all to me.

你本可以把它全部给我的。（本来能够做到，而实际却没做。）

You could have been a little bit tidier.

你本可以更加整齐一点儿。（本来能够做到，而实际却没做。）