You guys......
The answer to all this is right there in your own question. You ask what is the difference between a potential musical instrument and an actual musical instrument.
I suggest at this point that you find a dictionairy and look up the meanings of 'potential' and 'actual'.
There lies the answer that I have been attempting to get across. Anything further is just a case of argument for arguments sake.
I have faith in my own ability to reason and I know this is correct.
All the best, Gordon.