两个或两个以上简单句 （Simple Sentence） 可以合成一个较长的简单句、并列句 （Compound Sentence） 或复杂句 （Complex Sentence） .通过句子的合成，我们得以更清楚地看出句子间的语义关系，而且还可以使句子多样化，增加文章的丰姿。
（1） John ran away. He escaped the danger. → Running away， John escaped the danger. ）
（2） The hunter took up his gun. He shot the boar. → The hunter took up his gun to shoot the boar.
（3） The king died. The queen heard about it. She fainted. → On hearing about the king's death， the queen fainted.
（4） Kelvin is my good friend. He is a strong supporter of social justice. → Kelvin， a strong supporter of social justice， is my good friend.
（5） The rascal kicked the cat. He kicked it on the back. He kicked it intentionally. → The rascal kicked the cat on the back intentionally.
（6） John was sad. He kept quiet. → John was sad but he kept quiet.
（7） Take the book. Leave it there. → Take the book or leave it there.
（8） Sean did not come to class today. He had a bad headache. → Sean did not come to class today， for he had a bad headache.
（9） Bruce was lying on the bed. He looked at the ceiling. He saw a lizard. → Lying on the bed， Bruce looked at the ceiling and saw a lizard.
（10） Kelvin is getting rich. We know about it. → We know that Kelvin is getting rich.
（11） I like this book. It contains many amusing stories. → I like this book which contains many amusing stories.
（12） Helen is sure to get her pay. It is due to her. Why does she complain？ → Why does Helen complain since she is sure to get the pay due to her ？
（13） The woman was exhausted. She had not slept well the previous night. → The woman was exhausted because she had not slept well the previous night.
上面例子显示，简单句由“主语 + 谓语” （Subject + Predicate） 构成，有时还附有修饰性的短语。并列句由至少两个地位平等的并列分句透过并列连词 （Coordinating Conjunction） 如“ and， or， but， so， for ”等连成。复杂句包括一个主句 （Main Clause） 及至少一个从句 （Subordinate Clause） ， 通过从属连词 （Subordinating Conjunction） 如 “That， since， because， when， if ”等合成。从属分句因功能不同而分成“名词从句” （Noun Clause）， “副词从句” （Adverb Clause） 和“形容词从句” （Adjective Clause） .上述诸句式中，复杂句最为多采多姿，不妨多用。为了避免句子太长，难以控制，一个复杂句最好不要超过三个从句。