Choice of case when more than one is allowed

Question

Certain words govern more than one case even when the meaning is identical in both cases. For example, простить governs both the genitive and dative cases and «прости меня» and «прости мне» have the same meaning. I have a few questions regarding this phenomenon:

1. Is there a reason why more than one case is allowed (apart from ‘that’s just the way it is’)?
2. A Yandex search shows that «прости меня» is used much more frequently than «прости мне». Would usage of «прости мне» (or the less common case in any situation where more than one case can be used) send a certain kind of signal about your speech? (The closest analogue I can think of in English (which may not be a good analogue) is usage of ‘different than’ or ‘different to’ when others would use ‘different from’ (i.e. not in a context where most people would agree that ‘different than’ works better than than ‘different from’).)
3. Might the choice of case be regional or is it fairly evenly spread among the population?

Edit: It has been pointed out that the example is bad. I understand the difference between «прости меня» and «прости мне что-то» now. My question is about the choice of case when more than one case is permitted and both cases yield identical meanings; unfortunately I don’t have an example at hand now because what I thought was an example turned out not to be one. I would be glad to edit the example if someone can provide a valid example. I would appreciate it if future answers could address the question that I intended to ask. It’s possible that the question is vacuous because there is always a difference in meaning when both cases are used irrespective of the verb in question; if this is so, somebody can point it out and I would be happy to consider the question closed.

Answer 1

Sorry, a native Russian speaker here. I disagree with the premise of this question. "Прости меня" and "Прости мне" have a completely different meaning to me, albeit in a nuanced way.

"Прости меня" (who? -- "me" as a person) -- for example, "forgive me that I've been unfaithful to you" ("прости меня, что был тебе неверен") -- the subject of forgiveness is "I" as an individual

"Прости мне" (what?) -- e.g., "прости мне мои измены" (forgive me my transgressions)

The "прости мне" therefore has a somewhat deflecting, impersonal effect, perhaps comparable to "mistakes were made" in English -- a different grammatical structure completely, but the end result is also a "disappearing act" of the responsible party from the discourse.

Answer 2

1. Yes there is a reason for using these two forms. See below.

2. There is a certain "signal" when using прости мне instead of прости меня when it's allowed.

   Прости меня - say when someone want to be forgiven entirely and after that doesn't remain any reasons to be offended.

   Прости мне - say when someone want to apologise for a certain bad action(s).

3. The choice of case of the form прости is individual for everyone irrespective of localisation.

Answer 3

There are situations when two cases can be used interchangeably.

However, I would still like to expand on the discussion of your original example. "Прости меня." is a complete sentence, where "меня" is the direct object in accusative case. On the other hand "прости мне" is not a complete sentence. It is missing a direct object. It has to be "прости мне [something]", such as "прости мне мою грубость" ("forgive me my rudeness"). Notice that once you add the direct object, it is again in accusative case, while "мне" is an indirect object in dative case.

Grammatically, this is exactly the same construction as "дай мне книгу". "книгу" is the direct object in accusative, and "мне" is the indirect object in dative.