Student or Learner
"In the corner of the marketplace, an old man was playing a violin." (Azar grammar book)
Is the article before "violin" correct? I think it should be "the", not "a". Am I right?
“Mary is playing a/the piano in her room.”
In the case, we can only use “the”, not “a”. Am I right?
Either article works in both sentences. The choice of articles in this idiom is often somewhat arbitrary. Mary is playing the piano can mean either that Mary is engaged in the act of piano-playing or that she's playing a specific piano. Mary is playing a piano means that a piano exists, and Mary is playing it.
If Mary has a Steinway, a Fazzioli and a Büsendorfer, then you might say Mary is playing a piano in her room. She's playing the Fazzioli.
I am not a teacher.