因为since含有时间及缘故的双向实际意义，怎么使用才可以防止含意上的搞混?Since能用来表明缘故或时间，而这两个含意在应用上常常被弄混，请见下列词组：
A1 Since it was Saturday,I stayed in bed longer.
A2 Since she arrived,everything has been different.
词组A1中的since表缘故，A2的since则表明自某一时间点至今。
请记牢下列四个关键点：
Since的含意：无论是做为连词或者介系词，since的含意在于句子成分和语态。
Since做为连词：附设子句的形容词为过去时时，since一般表示时间。
Since做为连词：附设子句的形容词为如今式时，since一般表明缘故。
Since和for做为介系词：当恶性事件产生于某一时刻时，应用since;当恶性事件与一段时间有关时，则应用for。这时关键子句的形容词一般全是现在完成式。
Since：表示时间
Since一般做为连词(带入一个子句)或介系词(带入一个片语)，有时候也作为介词(单独存有)。
1.假如since子句表示时间，子句中的形容词务必是过去时。
B1 We haven't drunk anything since we got here.
B2 We haven't drunk anything since we've been here.
B3 I have been feeling sick(ever)since I ate that cake.
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2.在一个含有since子句(since you arrived)或since片语(since Tuesday)的语句中，若关键形容词指涉一段包括如今的期内，则该形容词务必为现在完成式。
C1 See examples B1–B3.
C2 I have been there since seven o'clock.
C3 Since winning the award,he has been really happy.
3.假如全句指涉以往的时间，则关键子句能以过去完成式。这时，since子句的形容词一般为简易过去时。
D1 We hadn't drunk anything since we arrived.
D2 I had been feeling sick ever since I ate that cake.
D3 I hadn't drunk anything since seven o'clock.
4.下列状况中的since皆表示时间：(1)since为介系词时(词组C2、D3)、(2)since后边接现在分词时(词组C3)。
5.Since还是for?
Since
做为介系词时只有与某一时刻配搭：这儿的时刻以介词(如：yesterday)、副词片语(如：the start of term)或姿势形容词(如：I ate…)表明。
E1 I've been here since last week.
Since
作为介系词时肯定不与一段期内配搭。
大家不能说since three hours，它是不正确的使用方法。
表时间的期内
是以for表明。
E2 I've been here for three hours.
当Since做为连词时，便可与一段期内或某一特殊时刻做配搭。假如表明一段期内，since子句的形容词一般是如今过去时(词组E3a、E4a);假如表明某一时刻，since子句的形容词则为简易过去时(词组E3b、E4b)。
E3a I've felt much better since the window has been open.
E4a He has lost weight since he has been running every day.
E3b I've felt much better since I opened the window.
E4b He's lost weight since he stopped eating chocolate bars.
Since：表明缘故
1.若since子句为如今式，则since必表明缘故，并非时间。
F1 Since it is raining,we are staying indoors.
F2 We will stay indoors since it is raining.
F3 Since he lives in Peru,he doesn't often visit us.
2.若关键子句及since子句中的形容词皆为简易过去时，则since一般表缘故，并非时间。
G1 I ate all the chocolates since you left them behind.
G2 Since he was poor,he never took taxis.
Since表时间时，关键形容词一般为如今过去时。
G3 I've eaten all the chocolates since I got home.