一個句子若以副詞片語或子句做開頭,那麼該副詞片語或子句的後面應使用逗點來與主要主句 (即獨立子句) 隔開。儘管有人認為可以不用,但使用逗點的主要目的是要讓句子易讀易懂,對於句意的正確傳達有很大的助益。不過,若句子的開頭並非副詞片語或子句,而是一個字的副詞 (如 Now, Today, Here 等),那麼它們的後面通常不用逗點。例如:
- In the center of Taipei, a lot of people fell victim to pickpockets. (在台北市中心,許多人遭到扒竊) (正)
- On Wednesday 2nd December, Jack broke up with his girlfriend. (12 月 2 日星期三,傑克跟他女友分手) (正)
- On Wednesday 2nd December Jack broke up with his girlfriend. (誤)
- When I was a kid, I would always swim in the sea. (小時候我常常在海中游泳) (正)
- After Jack had broken up with his girlfriend, he suffered from depression. (傑克跟他女友分手後得了憂鬱症) (正)
- Here they disagree with us. (在這一點上,他們和我們看法不同) (正)
- Yesterday Jack saw his ex-girlfriend having dinner with a man in a restaurant. (昨天傑克看見他前女友和一名男子在一家餐廳共進晚餐) (正)