For years I was taught that there were 4 gropus of musical instruments:
Brass
Woodwind
Strings
Percussion
This caused doubt as to the validity of the electronic organ because it made no sound on it's own. The turning of the tone wheels in a Hammond organ did nothing audible until a speaker was used...hence the debate.

In today's world of electronics and techinology, it is still a debate as to the validity of "things" that exist only in cyberspace, or in computer realm.

If an electronic organ is recognized as a musical instrument because it is played by a musician, then I suppose digital media is also valid...although, they still make no sound on their own. So,a better question is:

Are there only 4 groups of ACOUSTIC instruments? AIr has to move to make sound, but why does the intrument have to move the air alone?

My head hurts already.