冒号

1. 正确用法

从语法角度来说，冒号的作用与句号相同，都是表示一句的结束。然而，从语义的角度来看，冒号其实具有非常不同的功能，用以表示位于其两侧的句子间存在某种特殊的关联性。具体来说，冒号所表示的意义为，在其之前的句子具有“介绍”其后句子的作用。以下例句将说明冒号的典型用法。

1. We need the following ingredients: flour, eggs, milk, sugar and salt.
2. Each morning, the artist followed the same routine: wake at 6:30; eat breakfast; take a walk; review the previous day’s work; write down a schedule for that day; take a nap for one hour.
3. This model consists of four fundamental pieces:
   (i) diffusion terms;
   (ii) linear destabilizing terms;
   (iii) non-linear coupling terms;
   (iv) non-linear stabilizing terms.

正如上述例句所示，冒号表示位于其前方的文字在语法上已经完结。出于这个原因，冒号前方必须是一个完整的句子，而且就语法而言，必须与其后方的文字分开。不过，尽管如此，冒号前句子所表达的含义仍不完整，而且必须由之后的文字补足这项含义。

1. 错误用法

我经常遇到误用冒号的情形。在这类情况中，几乎都是因为冒号本身导致的语法障碍，进而形成语法错误。这类错误如下所示。

4. The main components of this apparatus include: (i) the primary reaction chamber; (ii) the secondary reaction chamber; (iii) the heating element; (iv) the exhaust mechanism; (v) the visualization mechanism.
5. This type of treatment has been found to work best for: diabetics, the elderly and stroke victims.
6. The milieu consists of: dendritic cells and T cells.
7. The first such relation is obtained as: x = a/2.

在上述每一句例句中，冒号都导致一个语法问题。在例句 (4) 中，冒号放在动词及其对象之间，而例句 (5)–(7)，则位于介词及其对象之间，这种语法结构肯定是错误的。以下列举一些修改上述错误例句的可能方法。

4. The main components of this apparatus include:
   (i) the primary reaction chamber;
   (ii) the secondary reaction chamber;
   (iii) the heating element;
   (iv) the exhaust mechanism;
   (v) the visualization mechanism.
5. This type of treatment has been found to work best for diabetics, the elderly and stroke victims.
6. The milieu consists of dendritic cells and T cells.
7. The first such relation is x = a/2.
   (7’) The first such relation is found to be x = a/2.
   (7’’) As the first such relation, we obtain x = a/2.
   (7’’’) The first such relation is derived as x = a/2.