Since 當連接詞用時引導附屬子句，意為「自從 (從過去某個動作或事件起到現在)，自 (過去某個動作或事件) 以來」。例如：
- It’s been twenty years since we married. (我們結婚到現在已經 20 年了)
- He’s been very busy since he went to work in Taipei. (他到台北工作後就一直很忙)
- Tony has known Cindy since he was 13. (東尼從 13 歲起就認識了辛蒂)
在 since 用作附屬連接詞來表示「自從 (從過去某個動作或事件起到現在)，自 (過去某個動作或事件) 以來」的句子中，附屬子句 (即 since 子句) 通常使用過去簡單式或現在完成式，而主要子句則使用現在完成式、過去完成式或過去簡單式，但以現在完成式居多。Since 子句無論使用過去簡單式還是現在完成式，意思並無不同。不過，要注意的是，若主要子句使用過去完成式或過去簡單式，則 since 子句須使用過去簡單式。例如：
- Adam has joined the Army for 12 years since he graduated from high school. (亞當高中畢業後從軍已 12 年了)
Adam has joined the Army for 12 years since he’s graduated from high school. - Robert had been composing music since he was nine years old. (羅伯特九歲起就開始作曲)
- I’d not seen her since she went to live in Kaohsiung. (她搬去高雄住之後，我就再也沒有見過她)
- It was the hottest October since records began. (那是有史以來最熱的十月)
如果主要子句的結構為 It + be + 時間 ( + since)，那麼 be 動詞可以是現在簡單式 is 或現在完成式 has been。這就產生了四種意思並無差異的句型。例如：
- It’s one month since a 9.0-magnitude earthquake and tsunami hit the island country. (那個島國發生 9.0 地震和海嘯至今已經一個月)
- It’s been one month since a 9.0-magnitude earthquake and tsunami hit the island country.
- It’s one month since a 9.0-magnitude earthquake and tsunami have hit the island country.
- It’s been one month since a 9.0-magnitude earthquake and tsunami have hit the island country.
在美式英語中，It’s been … since … 比 It’s … since … 來得常用。
事實上，在 It + be + 時間 ( + since) 的結構中，be 動詞亦可使用過去簡單式 was 或過去完成式 had been (兩者的意思並無不同)，但此時 since 子句須使用過去簡單式或過去完成式。例如：
- It was one month since a 9.0-magnitude earthquake and tsunami hit the island country. (那個島國發生 9.0 地震和海嘯已經一個月) － 指從發生地震和海嘯到過去某個時間點已經一個月。
- It’d been one month since a 9.0-magnitude earthquake and tsunami had hit the island country. (It’d = It had)
當 since 引導的是過去某一狀態 (而非過去某個動作或事件)，而這一狀態迄今仍然存在或持續，那麼 since 子句和主要子句都要使用現在完成式。例如：
- She has been living a hard life since she has been back to Taiwan. (她回去台灣後一直過著艱苦的生活)
- Since I’ve been away from the city, life’s been so much quieter. (我離開城市後，生活就一直清靜多了)
當 since 子句的主詞和主要子句的主詞相同時，我們可以省略 since 子句的主詞，此時 since 從連接詞變成介系詞，後接動名詞 (亦即主動詞變成動名詞)。例如：
- Since arriving in San Francisco, Helen has had over 20 job interviews. (自從來舊金山之後，海倫已經面試了超過 20 次)
－ 原句為 Since she arrived in San Francisco, Helen has had over 20 job interviews. - Since meeting at school, they’ve been friends. (他們自從在學校認識以來一直是朋友)
－ 原句為 They’ve been friends (ever) since they met at school.
Since 用作連接詞時還可引導表示原因的附屬子句，意為「既然」。Since 所引導的原因子句係表示不言而喻、顯而易見或已為大家所知的原因或既成事實的原因，通常位在主要子句之前，但有時亦位在主要子句之後。例如：
- Since you can’t answer the question, I’ll ask someone else. (既然你回答不出這個問題，我就問別人了)
- Since you feel tired, you should rest. (既然你感到疲倦，你應該休息)
- Since so, there is no more to be said. (既然如此，就再也沒有什麼好說的了)