prepositions - Are "in there" and "in here" incorrect?

We say,

1. Let's go home.


2. You belong here.

We do not say go to home and belong to here because prepositions and adverbs cannot be together. Then why the same rule is being violated by people saying "in there", etc?

Answer

You are correct that adverbs cannot be the objects of prepositional phrases. The issue at hand here is that many English words can act as multiple parts of speech. For example, "home" could be an adverb as in your example, but it could also be a noun.

Let's go home → "home" is an adverb telling "where" and modifying "go"

Let's go by home → "home" is a noun and the object of the adverbial prepositional phrase "by home"

The two sentences above have clearly different meanings. Sometimes however, the choice of whether to use an adverbial phrase or an adverb might not be as clear and the difference becomes more of a nuance rather than actual meaning. Take for example:

You belong here (with "here" acting as an adverb) versus

You belong over here" ("here" acting as a noun).

Both of these have essentially the same meaning. The only difference I can detect is the sense of closeness. I feel that "over here" conveys a sense of inclusion whereas "here" by itself is more of a statement of fact. "Over here" can also be used in cases where "here" is not close enough. I can picture a scenario where someone says, "You belong here...no, over here."

Put the book there versus

Put the book in there

Those two sentences can mean the same thing but in general, you'd use "in there" to specifically state that you're putting the book "in" something (like a box, or a house, etc).

Regarding your concern about "go to home" specifically, the best I can say is that "go home" is such a common expression that "go to home" does not sound correct. I don't think it is actually ungrammatical and a native speaker will understand you. To further complicate matters, if you modify home with an adjective ("Go to her home" or "Go to the second home" for example), it becomes perfectly acceptable.

"Belong to here" does not make sense because it is an incorrect use of the preposition "to" as it relates to the verb "belong". "Belong to" can only be used to show ownership in English and does not slow location. "It belongs to her" means that she owns it.