Definite articles (eg "the") indicate that it is a "known noun phrase" - the noun phrase is known by the listener/reader. Indefinite articles (eg "a") indicate an "unknown noun phrase" - the noun phrase is not one that is directly identifiable by the listener. But there are situations where there is no definite or indefinite article, such as when the possessive form is used. Consider the following sentence:

**1. A good idea of Tom's.**

We know that #1 is indefinite. But consider the following:

**2. Tom's good idea.**

Is "good idea" in #2 definite or indefinite? What is the deep structure of #2, above? Is it like "the good idea" (known noun phrase) or like "a good idea" (unknown noun phrase)?