請問can 和could的用法和分別

我想講, 樓上兩位都答得唔錯, could當然係 can既過去式,但係用法上係完全咁簡單架...

我諗問問題既人係比較想知usage上比較詳細既分別:

1 當解作可以/有能力, could就係can既past tense:
I can swim.
I can't swim now, but I could when I was young.

這樓上都已經詳細說明了....但還有很多can同could既分別:

2. could要在 reported speech (轉述)中代替can:
Sam: 'I can't go'
Sam said that he couldn't go.

3. 講未來發生可能性要用could:
I could come tomorrow if you want.如果你想,我明天可以來
比較: I can come tomorrow. 我明天能夠來(can係講有冇能力)

4. can同could在問句中語氣不同:
can係問能力 or 差唔多等於命令
could係問可唔可以(有禮貌)
比較: Can you fix your bed?? (這是阿媽講的,唔可以say no)
Can you drive? (問能力)
Could you help me on this? (問同事,有禮貌,唔係命令)

5. 建議某人可做某事,我地會講could have (done something), 但唔會講 can have
You could have met me at the station, couldn't you??
因為係建議, 係假設性既情況,所以要用 past tense既 could喇

就係咁....

can係普通既現在色！意思係可以！！可以講Ｉｃａｎ ｆｌｙ.
could係can既過去色！如果你話Ｉ　ｃｏｕｌｄ　ｇｏ　ｘｘｘｘ.（ｘ代表一個地方）
could既後面就唔洗轉過去色！！

could 係can既過去式
can指可以


could / can
你可以做到的！
You can do it ！(結果未知）
如果你努力一點，你可以做到的
If you worked harder, you could do it !（結果巳定了）


If you worked harder, you could do it 這個例子真的不太好
改一下：
could / can
If you practise more, you can pass the exam (考試還沒開始)
If you practised more, you could pass the exam. (考試結束囉，但沒及格)



If you have practised more, you could have passed the exam也是可以的
不過用have verb (pass tense)的發生時間指的是接近現在(now)，像說幾天前或一周前
基本上加不加have，大家都明白是過去意思了，只是加了have唸起來會有比較嚴厲的感覺