In Digest 970901 Ingmar Krause writes:

> By the way:  The minimum size to play a lot of music would be 12 notes,
> which is one octave.  (Now, who is going to discuss this with me? :)))

This reminded me of an entry in Pierce's Piano Atlas (p. 360), which
shows a picture of Bob Pierce and a spinet with 37 keys removed.  With
just 51 keys, "you can play almost any tune you can whistle or hum."

I believe most folk instruments are built on the 7-note diatonic scale
(harmonica, button accordion, concertina, dulcimer, etc.)  There are only
7 notes (not including the octave), and these instruments play lots of
music.  Hohner sells a "Little Lady" harmonica with 4 holes (8 reeds).
And then there are bugles....

In other parts of the world, the pentatonic (5-note) scale serves for all
their music.  American folk songs are often built on a pentatonic scale.
You can play many tunes with just the 5 black keys on your piano, such as
"Amazing Grace", "Swanee River", "Reveille", the Korean national anthem,
etc.

My nomination for "Minimum Notes Necessary to Play Lots of Tunes",
is ...  5.   :-)

Robert Linnstaedt

 [ I asked Steve Goodman why the diatonic (white-keys) scale was
 [ expanded.  He says it's because singers and singing groups
 [ finally realized that the "leading tones" were important, and
 [ so the ancient musical notation had to be changed to accommodate
 [ the new notes, and soon thereafter the first black keys appeared
 [ on keyboards.  ... Or something like that.  -- Robbie