Lesson 5 – Intervals Part 3: Perfect Intervals
The last thing I mentioned in the previous lesson (Lesson4 – Major & Minor Intervals), was that when inverted, major intervals become minor intervals. The Perfect interval, on the other hand, when inverted remains Perfect.
Hold that thought!
C – F (a 4th), is more specifically a perfect 4th, since F is in the key of C. If you lower the F 1/2 step to Fb , then the interval becomes a diminished 4th.
C – G (a 5th), is more specifically a perfect 5th, since G is in the key of C. If you lower the G 1/2 step to Gb, then the interval becomes a diminished 5th.
C – C is either a Perfect Unison (generally referred to as just “Unison”) or a Perfect Octave if the second note is 12 half steps higher than the first, (generally referred to as an “octave”).
The key things to remember here:
- 4ths, 5ths, unisons and octaves if *diatonic, are perfect 4ths, 5ths, unisons & octaves.
- Perfect 4ths or 5ths compressed by 1/2 step are diminished 4ths & 5ths.
(I suppose unisons & octaves technically are also, however I suspect that those spellings are a rarity).
*diatonic…..meaning within a key
B is diatonic to C, being the major 7th to C.
Bb is not diatonic to C.
NOW! Still holding that inverted perfect interval thought? As I said earlier, a Perfect interval inverted remains perfect. The reason this is true is because when inverted, Perfect intervals remain diatonic.
Example:
C – F (Perfect 4th, since F is diatonic to C)
inverted – F – C (perfect 5th, since C is still diatonic to F)
C – C speaks for itself.
Three more things to remember about perfect intervals when inverted…
1. 4ths become 5ths / 5ths become 4ths
2. Octaves and unisons remain the same
3. Perfect intervals remain perfect
Lastly, the augmented interval. Any Major or Perfect interval stretched by 1/2 step is an augmented interval.
1. C -D# (augmented 2nd)
2. C – E# (augmented 3rd)
3. C – F# (augmented 4th)
4. C – G# (augmented 5th)
etc…
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