Can
我们用can表达事情是可能的，或者某人有能力做某件事情。表达的构造为：
can+动词（can do/ see/ eat......）
We can see the park from our living room.
我们可以从客厅瞥见那个公园。
He can speak four languages.他可以说四种措辞。
有时候我们也会用be able to 表示”可以“，但是can 更常用一些，不过在现在完成时中，都是用be able to 来表示。
Tom can't sleep.（现在时态）
Tom 无法入睡。
Tom Couldn't sleep.（过去时态）Tom 无法入睡。
Tom haven't been able to sleep recently.（现在完成时态）Tom最近无法入睡。
Can的否定形式是：can not/ can't，表示”不能“。
I can't come to the party on Saturday.周六的派对我去不了。
同样，can't 也可以表示”以为某事不可能“
You can't be hungry, you've just had lunch.你不可能饿了，你才刚吃完午饭。
而表示”确定某事是真的“，则利用must。
John: My house is very near the station.（我的屋子非常靠近车站）Mike: Oh, it must be very noisy.（噢~那肯定很吵）
Could
之前有讲过，could是can 的过去时态，用于过去式的句子中，同样表示”可以“。它常常跟see，hear，smell，taste，feel，remember，understand一起利用：
He spoke in a very low voice, but I could still understand what he said.他用很小的声音说话，但是我还是能够明白他的意思。
When we went into the house, we could smell the buring from the kitchen.当我们走进房间的时候，可以闻到从厨房传来的烧焦味。
除了作can的过去式利用，could也可以表示”可能“，类似于may/ might。
The phone is ringing, it could be Jill.=The phone is ringing, it may/ might be Jill.
电话响了，可能是Jill打来的。
The weather is nice now, but it could change later.=The weather is nice now, but it may/ might change later.
现在景象很不错，但是一会可能会变天。
但是，couldn't 是不同于may not和might not的。
She couldn't have seen you, because she was too far away.她不可能看到你，由于间隔太远了。
She might not have seen you.她可能没有看到你。
疑问句中的Can/ Could/ Would...?
在表达”要求“”提出哀求“”容许“”约请“的问句，常日分别利用Can，Could，Would。
要求别人做某事时，常常利用can或者could：
I wonder if you could help me.Can/ Could you wait a moment, please?Can you do me a favour?Could you tell me how to get to the station?想要某些东西的时候，可以利用Can I have.../ Could I have...：
Can I have these stamps, please?我可以拿这些邮票吗？
Could I have a cup of tea, please.我想要一杯茶
在要求容许时，可以利用 Can，Could，May：
Can I speak to Tom, please?May I come in? --Yes, please.许可别人做某事时，最常用Can：
Yes, you can use the phone.是的，你可以用这部电话。
主动提出想要做某事时，可以用Can I...?：
Can I help you?Can I give you something to drink?约请别人时，我们可以用Would you like...?：
Would you like to come to dinner tonight?--"Yes, I'd love to."
