連接詞主要有 if， unless， as/so long as， on condition that 等。if 引導的條件句有真實條件句和非真實條件句兩種。非真實條件句已在虛擬語氣中闡述。

unless = if not. 例如：

Let’s go out for a walk unless you are too tired. 如果不太累，我們去散散步。

If you are not too tied， let’s go out for a walk.

典型例題

You will be late ___ you leave immediately.

A. unless B. until C. ifD. or

答案A.句意：除非你立即走，否則你就回遲到的。可轉化為 If you dong leave immediately， you will be late.B、D句意不對，or表轉折，句子如為 You leave immediately or you will be late.