使用 The 的時機

定冠詞 The 的使用時機：

1. 當名詞是特定對象，獨一無二時。
The is used with specific nouns. The is required when the noun it refers to represents something that is one of a kind:
例： the moon, the earth
但更精確來說*：世界上唯一的東西，不用the（例如 Mars, Venus, Japan）；世界上有很多的東西，要指溝通雙方都知道的對象，要用the（the sun）

2. 當名詞是抽象的概念時。
The is required when the noun it refers to represents something in the abstract:
例： the justice

3. 當指涉的名詞是之前提過的名詞時。
The is required when the noun it refers to represents something named earlier in the text.
例：A newspaper has an obligation to seek out and tell the truth. There are situations, however, when the newspaper must determine whether the public's safety is jeopardized by knowing the truth.


其他：

1. 在一般性指涉的用法 (generic reference) 中 a, an, the 都可以使用，並非只能用不定冠詞
例： A beagle makes a great hunting dog and family companion. / The golden retriever is a marvelous pet for children.


參考：http://grammar.ccc.commnet.edu/grammar/determiners/determiners.htm
參考*：http://blog.yam.com/studyenglish/article/7978177