插入语

• 前后用逗号与主句隔开。

• 删去句子总体意思不受影响。

• 可能一个词，一个短语，一个句子。

位置：主谓之间

放在实义动词之前，放在助动词之后。

Would,插入语,be

Had,插入语,done

作用：补充说明，以示客观

Dogs, it seems, love to chew up money.

He may even, in times of real need, do a little work.

These textbooks are , on the whole, small, presumably inexpensive to produce, but well set out and logically developed.

George showed me to the guest room which, he said, was rarely used.

作用：强调

Snails would, of course, be the main dish.

The reason, of course, is that costs have rocketed.

作用：强调重点内容（状语提前），避免头重脚轻

The linguist Joseph Greenberg has, since the 1950s, argued that all Native American languages belong to a single ‘American’ family (Since the 1950s).

The US great lakes region shares, with Canada, the second longest river systems in North American and has over half the coastline of United States (with Canada).

作用：强调（提前，补充说明）

But the costs to society can actually be quantified and, when added up,can amount to amazing sums (when added up).

The heroine had, in her youth, poisoned every one of her five husbands (in her youth).

作用：过度转折（连接副词）

Instead of becoming a doctor, however ,he became a successful writer of detective stories.

The study of the cultural history of smell is, therefore, in a very real sense, an investigation into the essence of human culture.