平行结构指的是单字或片语的形态相似。当句子或段落中的概念相似时，可以透过创造平行结构来强化意思上的相似性。有效的对句法需要能在句子中产生对称性，使文章更强而有力。对句法可以强调两个以上相似的概念。

平行结构的正确形式

下列的第一句包含平行结构，第二句则无此结构。

正确：The Editing Service Firm needs editors who are detail-oriented,who are self-motivated,and who are dedicated.

错误：The Editing Service Firm needs editors who are detail-oriented,motivate themselves,and exhibit dedication.

第一个句子中，who are重复了三次，使得detail oriented，self-motivated和dedicated三字具有相似性。第二的句子中，who are含有ambitious的涵义，但须拿掉are，以让读者了解句子内接下来的片语。当句子有正确的平行结构时，则不需要重复动词。

重复动词是风格和强调重点上的结构。不要过度使用平行结构!上述的句子一，不必用那么多的重复字，也可以表达意思。句子如下：

The Editing Service Firm needs editors who are detail-oriented,self-motivated,and dedicated.

使用对句法阐明意思

William researches cell membranes and walls.

Is William a biologist,or a biologist with an interest in architecture?This revision makes the meaning clear:

Janet researches cell membranes and cell walls.

使用对句法的一些方法

一系列中的事项：

As an editor,he revised,clarified,and rewrote.

成对的事项：

The musicians began not only to sing,but also to dance.

Ask not what your country can do for you;ask what you can do for your country.(John F.Kennedy)

列表和大纲：

The research had three main goals:To discover the cause of the disease.To propose a treatment.To document the success of the treatment.

把“Responsibilities included….”作为每个描述的开头，或用同一时态的动词作为每个描述的开端：如Researched、Conducted和Supervised。