1. Since從句為非延續性動詞的過去時或現在完成時，時間的起點應該從從句動作完成時刻算起。
例如：
Things have changed a lot since I wrote to you last time.
自我上次給妳寫信之後，情況已發生了很大的變化。
She has lived with us since she has come here.
自從她來到這裏，就壹直和我們住在壹起。
2. Since從句為延續性動詞的壹般過去時，表示動作或狀態的結束。其含義與動詞的詞義恰好相反，具有否定意味。
例如：
All has changed since he was at home.
自從他離開家以後，這裏的壹切都變了。
I haven?t written to her since she lived in London.
自從離開倫敦以來，我還沒有給她寫過信。
He has never been to see me since I was ill.
自從我病愈以來，他壹直沒有來看我。
Two years have passed since I last smoked.
我戒煙已經兩年了。
但如果since從句是延續性動詞的現在完成時，則表示動作由開始延續至說話的時候，具有肯定意味。
例如：
He has never been to see me since I have been ill.
自從我生病以來，他壹直沒有來看我。
She has talked little since she has stayed at home.
自從她呆在家裏以後，就很少講話。
Since we have owned a car， we have gone camping every year.
自從我們有了汽車後，年年都去野營。
3. 在現代英語中，since從句是延續性動詞的壹般過去時，有時候也可以表示肯定意味。此時，多半用ever來加強since的語義。
例如：
She has known me ever since she was a child.
她從小就認識我了。
I have live here ever since I was born.
我生下來就住在這裏。
4. 在it is+時間+since從句結構中，since從句是非延續性動詞的壹般過去時，含有肯定意味。
例如：
It is three years since her husband left her.
她丈夫離開她已經3年了。
It is over sixty years since the People?s Republic of China was established.
中華人民***和國已經成立60多年了。
5. 在it is+時間+since從句結構中，since從句是延續性動詞的壹般過去時，含有否定的意味。
例如：
It is three years since she stayed here.
她離開這裏已經3年了。
How long is it since you were a league member?
妳*有多久了?
6. 在it is+時間+since從句結構中，since從句是現在完成時或過去完成時，均含有否定意味。
例如：
It is five years since we have seen her.
我們已經5年沒有見她了。
It was years since I had seen her.
在那之前，我已經有好久沒有見到她了。
It?s been a long time since I?ve seen you.
我已經很久沒有見到妳了。
另
①根據英語慣用法，since從句不可以否定形式出現。
例如：
It is four years since I have smoked a cigarette. 我已經4年不抽煙了。
不可說：It is four years since I haven?t smoked a cigarette.
但由於下句中的since不作?自從?解，所以從句可以用否定形式。
例如：
I haven?t been out anywhere since I don?t know how long.
也不知多久了，我哪兒也沒去過。
②Since從句通常不與非延續性動詞的現在完成時的肯定式連用。
例如：
Her mother died when she was a child.
她小時候母親就去世了。
不可說：Her mother has died since she was a child.
③Since前不可加表示時間的詞語，但可以與ago連用。
例如：
She has lived with us since her mother died three years ago.
自從她母親3年前去世，她就壹直和我們住在壹起。
不可說：She has lived with us three years since her mother died.
④在It was five years ago since his father died. 壹句中的since用錯了，因為在含有ago的時間範疇裏，已經有了從過去的壹個時間點以來的時間，即已有了since的時間範疇，所以再用since是多余的。
改為：
It was five years ago that his father died.
他父親5年前去世了。
It is five years since his father died.
他父親去世已經5年了。