I know that technically, the prepositional (предложный) case is only used for objects of four prepositions: в (in), на (on), при (in presence of / at time of), and по (upon). However, can the prepositions be elided, for example, in dialog?
- О ком вы говорили?
- Маше.
To my non-native ear this sounds strange, but I wonder what native speakers would say. Can you provide good, natural-sounding examples where the prepositional case is used without a preposition?
No, as the name suggests, the modern prepositional case used with prepositions always. That wasn't so in old times, when there was a locative case, not a prepositional one. That is, all "natural-sounding" examples are about 500-900 years old.
Солнце ему тъмою путь заступаше;
нощь стонущи ему грозою птичь убуди, свистъ звѣринъ въ стазби;
дивъ кличетъ връху древа... (i.e. at the top of the tree)
What still remains in modern language is considered to be adverbs, like
Я возвёл очи горе́ --> I looked at the sky
Here горе́ actually means to the hill / mountain in a prepositionless form of locative case, but from the point of view of modern grammar it's an adverb.
This short-form answer (actually, dative case without additional context) to a question in prepositional case is impossible, it should be "О Маше". However, it is possible to answer indirectly - with an extended sentence where the subject in question is mentioned in any other case (dative here).
- О ком вы говорили?
- Маше отдавали должное - всё никак забыть её (выходку) не можем.
Sometimes a short indirect answer without a preposition can substitute for the subject meant in prepositional case:
- На чём поедешь, на телеге или в карете?
- Верхом (= на лошади, на ишаке).
