别东拉一句西扯一句了，你确定你是在写作文吗？

陈功

批作文的心情，有时候可以用悲喜交加来形容。好不容易看到个不错的topic sentence，大喜，觉得学生终于把自己的话听进去了。但是越往后看，心里越是拔凉拔凉的，因为后面的句子几乎都是东拉一句西扯一句，完全没有考虑topic sentence的感受。我们这再来回顾一下topic sentence的地位：

A topic sentence states the main idea of a paragraph. It is the most general sentence of the paragraph. All the other sentences serve to explain, describe, extend, or support this main-idea sentence. （Scarry & Scarry 2010:318）

你在定义里面看到“serve”这个词了吗？用大白话讲，topic sentence的地位一旦确立，其他句子都是为它服务的。

可见，写作文是非常有讲究的，光有Topic sentence还不够，其他句子要同样给力，才能保证这个段落不会被人找茬。但是很多同学写着写着就忘了自己要写什么了，比如下面的例子：

Eating out is always more expensive. The dishes are abundant and seem delicate. Because of the lack of supervision, food may be dirty and unhealthy in some not regular restaurants. Cooking dinner at home is cheaper as it saves the service charge. If you are not a professional chef you may not cook dishes looked so attractive but the dishes can be very safe.

上面例子出自学生的对比论证文，主要是对比在家吃饭好？还是出去吃饭好？这里的第一句话显然是topic sentence。它明确告诉我们外面吃饭不好，很贵。于是，我们满怀憧憬地想知道和在外面吃饭它到底贵在哪里了？贵了多少钱？可惜，当你继续读下去，你会发现，作者跑偏了…偏了…了…

不是说贵的问题吗？怎么又出现了饭店脏乱差的问题？还有饭菜的品色？敢情一点都没说贵的事情啊？

同学，你知道在写作中还有个词叫“unity”吗？下面请看定义：

Unity means that a paragraph discuss one and only on main idea from beginning to end. And every supporting sentence MUST directly explain or prove the main idea.

这儿有两层意思，一是一段话只说一件事；二是这段话里面的支撑句必须是直截了当地解释或论证这段话的主题。

这么看来上文的例子在unity（统一性）方面就很欠缺了。有同学可能会反驳，例子里面好歹有一句话说到了在家做饭可以节省服务费用了啊。但是，一句话远远不够啊！

我们还是来看一个unity好的例子吧。

In contrast with eating out, cooking by ourselves is cleaner and healthier. The foods outside usually have something to do with food safety problems. Take a glimpse at the exposure of the Eleme scandal. What behind those restaurants' bright appearances are the dirty kitchens that people cannot see, and people will never know how much food additives are there in the meals. Also, to make the food more attractive, the chefs tend to add more ingredients and oils, which really do harm to the cardiovascular system.

同样的写作任务，这个段落是不是看起来更加神清气爽一点呢？