she has a pretty face vs she has the pretty face

Question

My student asked me why we say "she has a pretty face" when describing someone. Is it possible to say "she has the pretty face" (we obviously have only one face)? And if not, how can we explain it? Can we apply the rule "The indefinite article is used with singular countable nouns to refer to a person or a thing that you are mentioning for the first time"?

Answer 1

To say

she has the pretty face

would suggest that there is only one face, or only one pretty face. In fact there are many possible faces. So one says:

she has a pretty face

which indicates that there are many possible pretty faces, and she has one of them.

In general when describing aspects of a person, one says in standard English

S/he has a/an {adjective} {noun}

and not a sentence using a definite article.