I have been trying to find out why the 4th and 5th intervals of a scale are called perfect. I understand the ratio business of the sound waves between the tones, but where did the term perfect come from and are the 4th and 5th really perfect? I think I see why the unison and octave would be considered perfect, but not the 4th and 5th.

Thanks

Dani
Sumner, Washington

______________________________

Perfect intervals invert to perfect intervals. They are also the lowest (first to appear, more importantly) in the overtone series. They are the purest, with ratios as follows:

Unison: 1:1
Octave: 2:1
Fifth: 3:2
Fourth: 4:3

Beyond that, I can't tell you where the term "perfect" came from. I suppose they could have been called "grounded" or "hollow" just as easily. Both describe their effect as well as, or better than "perfect."

As, or more, important, is understand the sound quality of perfect intervals, versus 3rds & 6ths, versus 2nds & 7ths. Chapters 15 & 16 in "Edly's Music Theory for Practical People" go into all of this in much more depth.

Hope this is of some help!

Edly
<http://www.edly.com>