wiesz, sama bylam ciekawa. Postanowilam zapytac native speakera - nauczyciela :) wychodzi na to, ze i ja mam racje i Ty po czesci.. kopiuje to co mi napisal:
''I've been playing the piano - Ongoing action in the past, with or without a definite end point.
'I've played the piano - Past action with definite end, but non-specific timeframe (specific timeframes = past simple, e.g. "I played the piano last night").
Compare "I've been playing the piano for the past five hours" with "I've played the piano for five hours straight several times before". The first sentence is ongoing, the second talking about a distinct occasion situated in the past, without specifying exactly when.
We also commonly use the present perfect continuous in contexts such as "I've been playing the piano for five years" - which of course does not mean without stopping.'
na zapytanie dlaczego mozemy powiedziec 'I've lived here for twenty years' i 'I've been living here for twenty years' i napisanie mu, ze tak naprawde te zdania maja to samo meaning i 'I've lived here' nie oznacza, ze juz tutaj przestalam mieszkac, a, ze przeciez nadal mieszkam - STILL. Odpisal:
'
Good point, they can indeed be used interchangeably in this meaning. To take your original example, either "I've played the piano for twenty years" or "I've been playing the piano for twenty years" could be used and would mean the same thing. Using the continuous form simply emphasises the ongoing quality of the action, as opposed to the duration (twenty years).
English past tenses are, I'm sure you realise, very complicated!'
:)