We’ve all been taught that most intervals are either major or minor… but that unisons, fourths and fifths are special intervals, considered “perfect.”
Let’s question that for a minute. I’m going to describe an alternative way of thinking about it that I think makes more sense. Not to convince anyone to adopt it—I’d say the standard terminology is more or less here to stay. But let’s consider an alternative just for the sake of shedding some sensible new light on harmonic ideas we take for granted. I think you’ll enjoy it.
The age-old terminology
Ok, so look at the circle of fifths:
Let’s label each note by its “scale degree” in the key of C. In other words, the interval formed by each note when it is placed above C:
We’re using the standard abbreviations for intervals: perfect (P), major (M), minor (m), augmented (A) and diminished (d).
Notice how most of the notes on the right side are major (green) and most on the left side are minor (blue). The exceptions are the perfect intervals P4 and P5.
Revamping the age-old terminology
What if we were to rename our perfect fourth and fifth?
What if we called them the minor fourth and major fifth instead?
At the bottom of the circle is the tritone. Instead of calling that note the augmented fourth or diminished fifth, let’s call it the major fourth or minor fifth.
Here’s a summary of the changes:
- perfect fourth → “minor fourth”
- perfect fifth → “major fifth”
- augmented fourth → “major fourth”
- diminished fifth → “minor fifth”
Ok, so why on earth would we want to do all that?
For starters, look what it does to the circle of fifths:
Everything clockwise from the root—the “bright” sounds—are now considered major.
Everything counterclockwise from the root—the “dark” sounds—are now considered minor.
The tritone, which can be either bright (the augmented fourth) or dark (the diminished fifth) depending on context, is now major or minor, accordingly. (I previously discussed these notions of bright and dark in a blog post called Harmonic Brightness & Darkness—you might want to check that out.)
Pretty nifty, no?A musical world with minor fourths and major fifths? Perhaps not as crazy as it sounds… #musictheory Click To Tweet
Look at what the new terminology does to the various modes of the major scale. First let’s look at all the modes, along with the notes in each scale, according to standard nomenclature:
Look at how much simpler and more systematic it is using the new terminology:
- The only perfect interval is also the only scale degree present in all the modes.
- The darkest mode, Locrian, is now made up of a root plus all its minor scale degrees.
- The brightest mode, Lydian, consists of a root plus all its major scale degrees.
The new system still preserves the rule that inversions of major intervals are minor intervals and vice versa: the inverted minor fourth is the major fifth, and the inverted major fourth is the minor fifth.
Lastly, the new system eliminates the need for the terms “diminished” and “augmented” in classifying intervals. Granted, one will still want to use those terms for various purposes (such as the diminished seventh interval), but now every interval can be named major or minor, with the exception of unison and octaves, which are perfect.
Without a doubt, this is a cleaner way of categorizing notes… and it makes our major/minor terminology align a little more closely with our notions of sonic brightness & darkness.
There are many possible objections. Let me field a few:
OBJECTION: “The unison, fourth and fifth are called perfect because none of the other intervals sound as pure.”
The unison is the most “pure” sound. Unison means two notes with exactly the same frequencies. Indeed, that is different from all other intervals, and deserves the unique label “perfect”.
After the unison, the octave has the simplest ratio – namely, 2:1. It too is considered perfect. I didn’t mention it earlier simply because adding an octave (or octaves) never affects an interval’s quality of major, minor, etc. Since unison is perfect, the octave interval is perfect too.
After those, the fourth and fifth have the simplest frequency ratios – namely, 3:2 (the fifth) and 4:3 (the fourth). But the major third (5:4) comes quite close; why not call that call that perfect as well? The purity of the fourth and fifth doesn’t put them in a qualitatively different class from the other intervals, just at one end of a consonance/dissonance continuum, of which semitone, tritone and major seventh are at the other extreme. We don’t have a special designation for those intervals; nor should we have one for fourth & fifth.
OBJECTION: The perfect fifth is contained in both the minor and major triad. If we called it a major fifth, a minor triad would have a minor third and a major fifth.
That’s true. But minor scales have lots of major notes. For instance, the Dorian, Harmonic Minor, Natural Minor and Melodic Minor scales all contain a major second. Yet they’re still minor scales. Major sixths and major sevenths figure into minor scales as well, and minor tetrachords. If minor scales and chords can contain notes we call major, it’s not clear to me that minor triads can’t be allowed to.
OBJECTION: The names major fourth and minor fifth are already in use to mean something else.
Yes. In quarter-tone terminology, a major fourth is midway between the perfect fourth and the tritone… and a minor fifth is midway between the tritone and the perfect fifth. It seems pretty clear to me that they just used those terms because they were available. In our use, the sound of the major fourth is the logical successor to the sounds of the major sixth, major third, major seventh, progressing around the circle of fifths. The quarter-tone use has no similar justification.
OBJECTION: Who cares? I’m used to things the way they are.
At some level I agree. But it’s also true that words have consequences, and our terminology shapes not just how we talk but how we think. I believe that if we did away with the concept of the perfect fourth and perfect fifth, kids would get to learn a simpler system that better reflects the sounds it describes… and they would be just a bit better set up for success in music.
Got an argument for or against that I haven’t touched on? Leave a comment. Or join the discussion on facebook.