同位语的四种形式有：名词以及短语（有时有逗号分开）、动名词短语（有逗号分开）、不定式短语（有时有逗号隔开）、形容词及其短语（有逗号隔开）。一个名词（或者其它形式）对一个名词或者是代词进行的解释或者补充，这个名词（或者其它形式）句尾同位语。同位语和被它限制的词汇的形式要一样，并经常紧挨在一起。
同位语的四种形式
1.名词及其短语(有时有逗号隔开)
A.George Bush，the present American president，was the governor of the state of Texas.
B.I want very much to read these new novels，especially the one you mentioned.
2.动名词短语(有逗号隔开)
A.He enjoys the exercise，swimming in winter.
B.Asking him to join us，that’s a good idea.
3.不定式短语(有时有逗号隔开)
A.There is one thing he’ll never do—tell lies.
B.The question what to do next hasn’t been considered.
4.形容词及其短语(有逗号隔开)
A.He，short and thin，is unfit for the job.
B.All the countries，big or small，are equal.
