a) 一般用于带有修饰语的名词词组前，但并非所有带修饰语的名词都需要the。例如：
Don’t you think Georgian houses are absolutely lovely?
Stainless steel (不锈钢器皿) has many uses.
I can’t say I care for modern art.
上面三句中斜体部分的名词虽然都有修饰语，因没有明确限定而是泛指一类事物，故不用the。下面三句斜体部分的名词则表示提到过的，特指的事物，要用the：
The Georgian houses have been sold.
The stainless steel was beautiful, but I thought most of the glass （玻璃器皿） they exhibited was rather unimaginative.
They showed a wonderful selection of the impressionists, but the modern art was too limited in its range.
b) 也用于有后置修饰语的名词词组前。例如：
The old houses which are most worth visiting are in the Imperial City.
The steel of the gun barrels has gone rusty.
The art of the eighteenth century has never been surpassed（超过）．
上面三句中的形容词从句和介词短语明确了是什么样的房子（what houses），什么样的钢（what steel）和什么样的艺术 （what art），故用the。下面三句同样有形容词从句和介词短语修饰名词，但是它们只指这些名词属于某一类事物，并非特指，故不用the。例如：
Houses which fail to satisfy these minimum requirements are to be pulled down.
Steel of great strength is needed for the manufacture of guns.
Art in the eighteenth century probably played a more important part in people’s lives than it does today.
EXERCISE 4
Fill in the blanks with the where necessary:
1. The engineers found that steel was of insufficiently high quality. Steel, I suppose, is the most important single product of the modern industrial world.
2. Large forests can have an important influence on climate.
Forests have all been cut down.