Man, I wish I had paid better attention to music theory. Or that I had Leonard Bernstein to teach it to me.
Here, he walks through the history of Western tonal music by moving through the harmonic series: The fundamental (C), the first harmonic (the octave, C), the second harmonic (the fifth above the octave, G), the third harmonic (the fourth above the fifth, C again), and the fourth harmonic (the third above the fourth above the fifth above the octave—E).
I guess the great thing about music is that you actually already knew all about these relationships. They felt right. But knowing why is great.
I need to find this whole lecture series.