意思不太一樣啊,
must是必須的意思,帶命令的語氣；should是應(yīng)該,表示建議；can是能夠,表能力但不一定是事實,need是需要.
我寫幾個例句吧：You must finish your homework before you go to play.你必須完成作業(yè)后才能出去玩.
You should tell him the truth.你應(yīng)該告訴他實情.
You can do it.你能夠做到.
We need light to read at night.晚上看書需要燈.
回答者：小Hey - 魔法師 四級 8-11 20:26
這四個詞都是情態(tài)動詞,具體區(qū)別如下：
must：
1）表示必須必要
You must come in time.
回答must引出的問句時,如果是否定的,不能用mustn't,而是要用needn't或don't have to.如
——Must we hand in our exercise books today?
——Yes,you must.
——No,you don't have to (you needn't).
2)must+be+表語的結(jié)構(gòu)表示有把握的推測,他的否定或疑問形式用can代替must.如：
This must be your pen.
should:
1)表示勸告、建議、命令,其同義詞是ought to.在疑問句中,通常用should 代替ought to.如
You should go to class right away.
Should I open the window?
2)表示應(yīng)該做,且有一種道義上的責(zé)任.如
I should help him because he is in trouble.
3)表示明顯的結(jié)果或合理的推斷,且所期待的是幾乎是事實,因此不是虛擬語氣.
Mary took dancing lessons for years; she should be an excellent dancer.
It is three o'clock,the football game should begin soon.
4）疑問句中,should表示不合理,難以相信或不應(yīng)該的事,意為“竟會”,常與how,why,who 等聯(lián)用.如
Why should he publish such a book?
5)用在I'm surprised ;You can't imagine 等結(jié)構(gòu)中,表示驚訝,憂慮,惋惜等情緒.如：
You can't imagine that a well-behaved gentleman should be so rude to a lady.
can:
1)表示能力,如
Can you finish this work tonight?
2)表示請求和允許.如
Can I go now?
3)表示可能性,如
We can call for you at nine.
4)表示推測某一事物某一時的情況,如
Our house is on the top of the hill,and in winter the winds can be pretty cold.
5)表示驚異、懷疑、不相信的態(tài)度（主要用在否定句、疑問句或感嘆句中）如
Can this be true?
need:
1)表示“需要”或“必須”,做情態(tài)動詞用時,僅用于否定句或疑問句.在肯定句中一般用must,have to,ought to 或should 代替.如
-Need I finish the work today?
-Yes,you must.
2)作實意動詞時,又人稱、時態(tài)和數(shù)的變化.
They did not need to arrive so early.