I know how to play / blow a flute.

[billmcd]

I was thinking more of removing 'the' and using 'a', because to me, in some cases, 'the' sounds like they are referring to a specific flute/guitar/piano.

"The" would be used in that context to identify the instrument as distinct from other types of instruments, but "a" works too.

[bhaisahab]

"The" would be used in that context to identify the instrument as distinct from other types of instruments, but "a" works too.

I play the Irish Whistle, that's the type of instrument I play. I own several of them and I don't always play the same one. It would be wrong to say I play an Irish Whistle.

[emsr2d2]

I play the Irish Whistle, that's the type of instrument I play. I own several of them and I don't always play the same one. It would be wrong to say I play an Irish Whistle.

I agree. If someone said to me "I play a flute" I would be tempted to ask "Which one?"

[Winwin2011]

We generally use "the" when talking about the ability to play a musical instrument.

I can play the flute.
I play the guitar.
He plays the piano.

Some people omit the article completely.

As far as the original question goes, I would avoid using "to blow" when talking generally about musical instruments. Even though that is how some of them are played, we don't use it that way very often.

Does it mean "Can you play a guitar?" is not natural? I remembered a native speaker asked me, "Can you play a guitar?'

[bhaisahab]

Does it mean "Can you play a guitar?" is not natural? I remembered a native speaker asked me, "Can you play a guitar?'

I'd say it's unusual. I'd expect to hear "Can you play (the) guitar?"

[emsr2d2]

Does it mean "Can you play a guitar?" is not natural? I remembered a native speaker asked me, "Can you play a guitar?'

I would not find that natural at all and would be surprised if a native speaker said it.

[HanibalII]

I agree. If someone said to me "I play a flute" I would be tempted to ask "Which one?"

Isn't 'the' the same though?

It doesn't specify which flute.

[Chicken Sandwich]

Isn't 'the' the same though?

It doesn't specify which flute.

NOT A TEACHER

I think that with "the" it's a general statement, it refers to one's general ability to play a particular type of instrument. 'I play a flute' is an unusual statement (and I don't think I have ever heard it). It means to me that the speaker only plays one specific flute.

[emsr2d2]

I don't deny that sometimes our constructions are not logical. For example:

I can drive a car.
I can play the flute.

My brother learnt how to drive a lorry when he was 17.
My sister plays the drums, the clarinet and the guitar.

Can you drive?
I have a licence to drive a car, but not a motorobike.

Obviously, when we say "I can drive a car" we don't simply mean we can drive one car but not any of the other millions of cars in the world. My brother didn't learn to drive only one lorry.
However, those are the terms we use and no, I can't explain why.

[Tan Elaine]

I'd say it's unusual. I'd expect to hear "Can you play (the) guitar?"

Is 'the' optional?