Is 'there' an adverb or a preposition? (Or something else entirely!?)

Solution 1:

As is well-recognised by linguists, dictionaries are not a good place to start when trying to establish parts of speech. A good reference grammar is. Of the three great grammars of the English language from the last hundred years, the most recent and up-to-date is The Cambridge Grammar of the English Language, Huddleston and Pullum, 2002. It says the following:

Locative there is an intransitive preposition contrasting with here: it has deictic and anaphoric uses ... (p. 1319)

(For a fuller account, consult pages 598-691). Part of the reason given for there and here being prepositions is that, exactly as OP has commented, they are modifiable by straight and right. Furthermore, these words function in the same way as other prepositional phrases: they are able to function as locative complements of the verb BE, and also as spacial and temporal adjuncts.

Many phrase types have the latter function, including adverbs and adverb phrases, however adverbs don't generally function as complements of the verb BE. Furthermore adverbs are not modifiable by either right or straight:

Complements of BE

• The comments were erroneously. * (adverb complement)- wrong
• The comments were locally. * (adverb complement)- wrong
• The comments were out of order.
• The comments were at the bottom.
• The comments were below.
• The comments were here.
• The comments were there.

Straight and right as modifiers.

• He flew straight beautifully. * (wrong)
• He flew right directly. * (wrong)
• He flew straight to Paris.
• He flew right over the house.
• He flew straight in.
• He flew straight there.

This all goes to show that the OP is indeed correct: there does indeed seem to be a preposition.

Hope this is helpful

Solution 2:

First a caveat: you cannot always reliably test what function a certain word or phrase has by replacing it with some other word or phrase. However, normal adverbs serve the same function as many prepositional phrases do, so what you said about how it can replace in Paris supports treating there as an adverb.

A preposition occurs before a nominal phrase, like a noun; but there Paris is not possible, unlike in Paris. And so it is not a preposition, unlike the preposition in.

There is often called an adverbial demonstrative pronoun. While it does normally have an adverbial function (it describes where something happens), it has an antecedent: it refers back to a place that was mentioned earlier or that the listener or reader knows is relevant. So in your example, it refers back to Paris, a place; in its capacity of referring back to an antecedent, it is pronominal, functioning like a pronoun.

It is demonstrative because you can point at something while saying it, just like the demonstrative (personal and adjectival) pronouns this, that, those and these: I see that [pointing at object], we went there [pointing at place] etc.

Note that, in certain idiomatic constructions, there has almost evolved into something more like a particle, as in there was noöne in the room.

The words straight and right in your example are a bit complicated; they could be analysed in different ways. The two most obvious ways would be to either classify them as adverbs modifying there, or as adverbs modifying the verb in parallel with there. The simplest structure of I flew straight there would be the latter: how did you fly? I flew straight, not via some other point. Where did you fly? There. Those are two adverbs, one of manner and one of place/destination.