We have already looked at intervals and you now know that going from C up to G, for example, is called a “perfect fifth” interval.
But you can also go from C down to G. What is that interval called? Hint: it’s not a fifth.
As before, you can count the number of half-steps going down from C to G. Or you can take the elaborate method of counting the number of notes and adjusting for sharps and flats.
But there is another way: you can invert the interval from C-up-to-G to get the interval from C-down-to-G.
Here is the rule: inverted interval = 9 – interval
Fortunately, that is not too heavy on the mathematics. So C-down-to-G is: 9 – 5 = a 4th.
The 5th was perfect. Is our 4th also “perfect”?
A few more rules:
- Perfect intervals remain perfect.
- Major intervals become minor.
- Minor intervals become major.
- Augmented becomes diminished.
- Diminished becomes augmented.
So inverting a perfect fifth indeed results in a perfect fourth, and vice versa.
Another example: the interval C up to A. This is a major sixth. If we invert this interval, we get 9 – 6 = 3 and major becomes minor. So C-down-to-A is a minor third.
To find an interval in the opposite direction, you can also reverse the notes. Instead of doing C-down-to-G you can consider this G-up-to-C, which is identical. Likewise, C-down-to-A is equivalent to the interval A-to-up-C.
Fun, fun, fun.
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