“Is there a best X?” — why “a” if it's the superlative degree?

Question

Which of the following is grammatical?

1. Is there a best school?
2. Is there the best school?

I'm sure that the first one is right. But why?

Answer 1

The is the definite article. A is the indefinite article.

The question "Is there a best school?' is, by its nature, indefinite. Ergo, a.

EXPANDED ANSWER:

It is necessary to determine the meaning of the question. Does it mean

1. Does there exist a school that we would consider to be "the best"?
   or
2. Is the best school (which I know exists) in the particular location to which I am pointing?

Without more context, most native English speakers would interpret the question as in number 1. In that case, the declarative form of the sentences would be

There is a best school.

This is an adverbial use of there meaning

(3.) (usually there is/are) used to indicate the fact or existence of something: there comes a point where you give up

The sentence means that a best thing exists, but we are not indicating which particular school is best. The reference is indefinite as to which school merits the title, so the indefinite article a is used.

If the intended meaning is that described in number 2, the declarative sentence would be

There [pointing] is the best school.

In that case, there is used as an adverb meaning

(1.) in, at, or to that place or position: we went on to Paris and stayed there eleven days

If that was what was intended, a particular school is being identified, and the definite article the would be used. However, most English speakers would not use this construction.