WAV - If you've got one of those electric keyboards with various voices, choose one with a sustain - organ, flute or violin. Forget about the black notes for now, and imagine the white notes as a pure diatonic Pythagorean scale - though of course it's tempered, which is to say perverted for the sake of western chromaticism so that lot of the intervals are far from pure.

Take a piece of insulating tape and tape down one of the keys as a drone, try the D to begin with, and play a scale using only the white notes between D & the next D. This is a mode - the Dorian Mode to be precise - which has unique musical characteristics beyond either what we might conventionally think of as either Major or Minor. C to C is a Lydian Mode, which is identical to the major scale, each note of which Lydian Mode can become a drone for another mode - D gives Dorian, E gives Phrygian etc. each with their own characteristics largely forgotten in Western musical theory. From hereon in, the territory gets interestingly archaic, but essential, I would think, to any understanding of folk music, which is inherently modal and monophonic, though in no way, of course, does this preclude harmony, or yet heterophony.

For more on this see:

http://en.wikipedia.org/wiki/Musical_mode