mustnt have done与cant have done区别

Question

如题所述

Answer 1

一、cant have done 是 must have done 对过去推断的否定形式。

二、具体说明如下：

情态动词 must （必定、一定）”表示推断或指具有较大的可能性时，其否定式是 can't/cannot (不一定、不可能)。

1. 对现在的推断

* 肯定 —— must + be， 如：
You must be very tired. 你一定很累了。

* 否定 —— can't + be, 如：
You can't be very tired. 你不一定很累。

2. 对过去的推断

* 肯定 —— must + have done， 如：
He must have earned a large sum of money. 他一定是挣了一笔巨款。

* 否定 —— can't + be, 如：
He can't have earned a large sum of money. 他不可能挣到一笔巨款。

三、关于 mustn't

mustn't 地意思是“不准许、]禁止”，mustn't have done 意思是“绝对不允许已经做过、绝对禁止做过”，不表示推断。因此与 can't have done 没有直接关系。

Answer 2

mustn’t have done是很肯定的猜测语气
can't have done 猜测没有那么肯定，一般不用can't 而是用may not