同位語的四種形式有：名詞以及短語（有時有逗號分開）、動名詞短語（有逗號分開）、不定式短語（有時有逗號隔開）、形容詞及其短語（有逗號隔開）。一個名詞（或者其它形式）對一個名詞或者是代詞進行的解釋或者補充，這個名詞（或者其它形式）句尾同位語。同位語和被它限制的詞匯的形式要一樣，并經常緊挨在一起。

同位語的四種形式

1.名詞及其短語(有時有逗號隔開)

A.George Bush，the Psent American Psident，was the governor of the state of Texas.

B.I want very much to read these new novels，especially the one you mentioned.

2.動名詞短語(有逗號隔開)

A.He enjoys the exercise，swimming in winter.

B.Asking him to join us，that’s a good idea.

3.不定式短語(有時有逗號隔開)

A.There is one thing he’ll never do―tell lies.

B.The question what to do next hasn’t been considered.

4.形容詞及其短語(有逗號隔開)

A.He，short and thin，is unfit for the job.

B.All the countries，big or small，are equal.