the/a right person and the tallest person

Why is it 'tallest person' always only takes 'the,' and that 'right person' may sometimes take 'a' depending on what you mean?

I don't know how I should put it, but the 'comparative superlative + noun' and 'right + noun' are said to require the definite article 'the.' However, while the former always calls for 'the,' the latter sometimes licenses the use of 'a/an' when there are a lot of 'right' people etc. although, granted, most of the time 'the' is attached. What do you think makes the difference?

He is the tallest person in the class. [Nobody is the same height or higher]
He is one of the tallest people in the class.
~~He is a tallest person in the class.~~ [NOT IDIOMATIC]
He is the right person to ask the question.
He is a right person to ask the question. [There are many other right people who could answer it]

EDITED: superlative >>> comparative superlative + noun

Solution 1:

Before you ask the 'why' question, I think you should set the facts straight first.

...the superlative always calls for 'the'...

That's not true, because both these superatives all sound fine without the definite article:

(1) He is tallest in the class.

(2) Last week, no less than 76 per cent of the public said that the spread of the virus was the story to which they had paid most attention. (The Times)

(3) The Korean thriller “Parasite” has become the first non-English language film to win the Oscar for best picture. (New York Times)

Therefore, it's not the superlative itself that requires 'the'.

What requires 'the' is the 'superlative + noun' combo where the presence of the superlative makes the noun phrase definite in context.

Solution 2:

Typically the superlative expressed with most or –est requires a definite article because the semantics of the superlative requires a unique element. So in a context where there are two equally tall people in the room, it's infelicitous to say (1)

Arthur is the tallest person in the room.

This is typically true of how the definite article works in English independent of the superlative. The definite article usually picks out a unique individual in the context. For example, the following is also an infelicitous use of the definite. (The # symbol is used to mean "inappropriate for the context".)

Arthur and Bob came into the room. #The man sat down.

So the use of the definite in the superlative follows from the fact that there is a unique individual who satisfies the description.

It's not true, however, that the superlative requires a definite article. For example, suppose we are inquiring about the heights of the players on a basketball team. It's perfectly reasonable to say (3):

Does this team have a tallest player?

Here, uniqueness is what's being questioned, and so the indefinite article is used, and the definite is impossible. Similarly, if we were evaluating all the teams in a league, we could felicitously say something like 4.

Every team except two has a tallest player.

In these cases the uniqueness requirement of the superlative is being evaluated relative to each team, so these noun phrases could be paraphrased as "a player who is the tallest one on that team".

The preference of the definite article with adjectives like right and wrong is again due to the fact that there is a presupposition that there is a unique right or wrong answer in the context, but this isn't really built into the meaning of these adjectives. Any time this expectation is not met, the indefinite article will be able to be used: