什么时候can或could可以表示肯定的推测？

Question

can/could 多用于否定的和疑问的推测；一般不用于肯定的推测。但有时也用于肯定的推测，比如It can be true！或
A：I've taken other's sweater by mistake.
B: It could be Harry's. He always wears green.
但我想知道什么条件下can或could可以表示肯定的推测？

Answer 1

一、CAN

1.1 表示有能力：

Sam can play the guitar.
Can Howard sing?
He can't (cannot) understand German.

1.2 表示许可：

Can I park my car here?
No, you can't, it is a no parking zone.
Can I go to the theatre with Zhang?

1.3 表示可能：

A car can be a useful means of transport or a dangerous weapon.
She can be very hard to understand sometimes.
We can live life with a positive or a negative attitude.

1.4 在否定或疑问时，有"何至于"，"不可能"之意：

He cannot be a cruel man. 他不可能是一个冷酷的人。
Can they have said such a thing? 他们何至于说出这样的话？

二、COULD

2.1 作为can 的过去式：

She couldn't (could not) come to dinner last night.
They could walk faster when they were younger.
Sam could play the piano when he was a boy.

2.2 客气请求：

Could you tell me the time, please?
Could you help me, please?
Could I have a coffee, please?
Could we come and visit you this evening?

2.3 could not help-ing, could not but 有"不禁"，"忍不住"之意：

We could not but laugh. 我们忍不住发笑了。
We could not help laughing. 我们不禁笑了起来。

谈起助动词感到真有点枯燥，可是它们在英文里作用可大呢。希望大家一起学习，一起
进步。再见。

Answer 2

在一般现在时和过去时的陈述句中,就可以表示肯定本回答被提问者采纳