But it's still where the generic, simplistic application of the rule of "the for distinct, a for generic" fails. When "you can play the piano", you can play an

But it's still where the generic, simplistic application of the rule of "the for distinct, a for generic" fails. When "you can play the piano", you can play any piano. When "there is a piano in the lobby", it's distinctively a very specific one. So I would go on a limb and claim: whether you use the or a is also philosophical in nature :)