Why Some INTERVALS Are Major Or Minor While Others Are Perfect?

Why Some INTERVALS Are Major Or Minor While Others Are Perfect?

Tommaso Zillio

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major minor perfect intervals

Question I got recently: "Is there a good reason why we call some musical intervals ‘perfect’, while some are called major or minor?"

For instance:

  • a 3rd could be major or minor...

  • ...but a 5th can not be major or minor. You can have a perfect 5th, and if you really insist, you can also have a diminished or augmented 5th - but no major or minor 5th for you, no sirree!

(As you'll see in the video, this is because all the major and minor 5ths were handed out in the 18th Century, and we are left just with the perfect ones. True story!)

That looks puzzling, doesn't it? I know it confused me to no end!

There is, in fact, a reason for this, and as with most things in life, it’s probably easier to just not question it. Assume there’s a good reason, blindly follow authority, live your life in a state of blissful ignorance.

Nah, just kidding :-)

Of course you don’t want to do this. If you are subscribed to this newsletter, you have a curious mind and want to seek out new knowledge wherever you can find it, so you can learn and grow as a person, and become a better version of yourself. Like some kind of nerd.

In that case, from one nerd to another, I’ll first give you the obvious, reasonable, and wrong explanation:

  • The name perfect, as opposed to major or minor, is used when an interval remains the same in both major and minor scales.

  • Intervals that change between these scales are given the terms major and minor.

Ah, wouldn't it be great if life was so simple?

But you may already have spotted the problem: "Then why don’t we call 2nds perfect since they stay the same between major and minor?"

Great question!

For that, allow me to direct your attention to the video below, where I’ll explain the correct difference between perfect intervals and major/minor intervals.

Watch the video here, and you'll see that everything makes "perfect" sense (pun intended):

Understanding intervals is especially important for furthering your knowledge of chords. If you want to learn more about chords and harmony on guitar, check out my Complete Chord Mastery guitar course.

Video Transcription

Hello internet, so nice to see you! Some months ago, a student asked me why we call some intervals like fourth and fifth perfect. And why we call some other intervals like thirds and sixths and seconds and sevenths major and minor.

Well, the answer accepted today is that the first of all is just to name a second is because there are two versions of say the third major third minor third, while there is only one version of the fifth, which is not really true, since we have the augmented fifth and the diminished fifth, but let's gloss over that for a moment. And another reason is because a perfect interval tend to be more consonant than other intervals.

So fifths fourths, and octaves tend to be much more consonant. So we want to give them a different name. That's the answer I gave him. But honestly, there was this little voice inside me, telling me no, this is not the actual answer.

A few months later, I was reading an Italian Baroque manuscript. And I discovered to my utter surprise that they were talking about major fifths, and minor fifths. Oh, my, if today somebody said major fifth on YouTube, that person will be crucified in minutes by a horde of YouTube trolls. So what was happening there, why they were calling fifths major and minor, and later, I found also there were major and minor fourths.

What was happening there? Well, that's interesting, because in Baroque music, you actually have two version of the 50. And two version of the fourths. The major fifth, is what today will call the perfect fifth and the minor fifth will be the diminished fifth. And for the fourth, what do we call the perfect for to be a minor fourth. And what today because our augmented fourth will be a major fourth, this actually makes a lot of sense.

And understanding why they were calling in service this way. And how we got to change to our current names, really clarifies a lot about the inner work of music. So let's see what's happening here, let's put ourselves in the mind of a Baroque musician, we're going to have the major scale, C, D, E, F, G, ABC, just we're going to get the A and C, because everybody knows that. And we have, of course, our notes in between those notes.

And let me write on top, how many half step there are between the first note C and all the other. So if you look at it this way, it's very easy to number the notes of the scale, meaning the C is the first D is the cycle, and the E is the third, and so on and so forth. And if we compare these with a minor scale, you see that, for instance, the third sixth, and seven exists in two versions.

So it's very easy to group those and call one of them the major third, and one of them the minor third, one of them the major sixth one, the minor, one, and then the major seventh one, the minor. That's fantastic. What about the other intervals? Well, the second is the same for both major and minor, but it still makes sense to call one of them major second and the other minor second, because they have pretty much the same pattern as the other. The fourth and fifth are a bit more complex.

Because, you see, they seem to overlap because thinking like Baroque musician, they were using the triad on the note in between the fourth and the fifth, often, and sometimes that we're getting the strike on by taking an interval of a fifth and lowering the top note, and some time by taking the interval of fourth and raising the top note.

So they really wanted to distinguish those two situations, they really wanted to be clear on which one of the two was happening, because in Baroque music, it's important to know, because it changes the way you resolve the dissonance, the G flat will resolve down and the F sharp will resolve up this by the way, it's still true in music today, though, of course, we can break these rules anytime we want.

And they could break Israel anytime they wanted. But they just wanted to be clear on that. So they were thinking of the fourth and fifth that's overlapping, the G and G flat would be major and minor fifth, with the higher one being called major and F and F sharp was still major and minor four, with the higher one being called major.

So far, so good. Now notice that this system as a very pleasant property, if you want to invert an interval, you just subtract the interval from nine and invert major and minor. What do I mean with that? Well, let's take a major third C to E. If rather than thinking C to E, which is a major third and thinking e to the next note C, I will have a different interval.

To know what is this interval, I need to take the number nine take out three because the original interval was a third so I get a 16 and then invert major and minor. So the original was a major third, the inversion is a minor sixth. And this is true everywhere. So the inversion of a major second is a minor seventh inversion of a minor second ism major seven, and so on and so forth.

And notice that the inversion of a major fifth is a minor fourth, and the inversion of a minor fifth is a major foot, everything works perfectly, it makes perfect sense. And that went on for all the 18th century, then somewhere in the 19th century, they decided that they didn't like this naming system anymore.

Now the exact reason that's difficult to find, I've been reading a lot of original books from the 18th century in the 19th century, and nobody ever explains to you why they're doing things and why they change the names. But I think I got a good idea of what was going on in their mind. One of the things I didn't like is that the fourths and fifths were overlapping why none of the other intervals is overlapping.

The other problem is that both major third and minor third are consonant and both major six and minor six are consonant, both major seven A minor, seven dissonant and both major second and minor second that dissonant, but for fourth, and fifth, this doesn't happen. The major fifth is constant, and the minor fifth is very dissonant.

The minor fourth is consonant and the major fourth is very dissonant. And that's kind of a mismatch that people really didn't like. So they set out to find a different system. And the idea was, well, let's call those perfect. Now, this does not happen. From one day to another, there was a lot of trial and error, a lot of academic discussion, you can trace lots of scattering letters from one theories to another because one was obviously right one was obviously wrong.

But eventually, they landed on the system we have today. How is our system different? Well, we divide the internals in flexible and inflexible the flexible interval are second, third, sixth and seventh that exists in both major and minor version, but they can also exist in augmented and diminished version.

If you expand the interval another step from major you get an augmented interval, if you shrink it from minor, you get a diminished interval. So for instance, you can have a diminished seventh, which is B double flat, which is yes, and harmonically the same as a but formally a different one.

And then we have the inflexible intervals that have only one version, the perfect one, but then you can still create augmented and diminished version. If you go from perfect and expand the interval one half step you get an augmented interval. And if you shrink it from perfect by one half step, you get the diminished interval.

So now the G will be a perfect fifth to the G flat will be a diminished fifth and the G sharp in harmonically equivalent to an A flat will be an augmented fifth. Now this new system still allows to invert intervals using the rule of nine so I can still subtract the interval from nine. And now though major invert minor minor invert to major perfect invert to perfect, diminished invert to augmented and augmented invert to diminished.

So if for instance, if I have a diminished fifth, nine minus five is four and diminished, invert government doesn't have an augmented fourth. So see, the new system works perfectly to pun completely intended, it's just different than the one before, if I were to look at both the systems with fresh eyes and forget for a moment that I was taught the modern system.

And so if you say major fifth to me, I have a fleet of ragers for you labeling things incorrectly, like the worst troll on YouTube. Well, looking at them with fresh eyes, the original Baroque system was actually easier to learn, because you had only two things to learn major and minor. And you could still think about augmented or diminished interval if you wanted in specific case like the augmented sixth chord, which happens occasionally, actually pretty often in Baroque music.

But it was easier and in this sense more coherent more, if you want more adapted to the human mind, because you just have to version of every interval period. But the modern system is more mathematically correct. And it also more perceptually correct, because the fifth and the fourth do sound different than the other intervals.

And you cannot just say that what we call today, the perfect fifth and the diminished fifth are just major, A minor version of the same intervals. Those two notes those two intervals, sound radically different. One is extremely consonant one is extremely dissonant, much more than the difference between say major and minor third, and major and minor seventh.

So the modern system recognizes that we do perceive those intervals differently, and it clarifies it directly in the name, perfect major or minor. At the end of the day though both system works perfectly well. Both system allow people to make music. And it's pretty much an aesthetic choice. I will not advocate going back to the baroque method when everybody today uses the modern method, I mean, there will be just confusing.

And then again, you will run the risk to occasionally say things like major for two and then everybody will stab you with their pointy guitars. But that's the real story of why we call some interval perfect and some other intervals major and minor. And then No, you guys at this point are waiting for me to give you the moral of the story.

But in real life, often stories don't really have a moral except maybe, that the system is not that important, as long as you can make music with it, and you understand the sounds behind the name. So that the major third is not just the major third, but it's these and if you understand that, then you have everything you need. This is Tommaso Zillio for MusicTheoryForGuitar.com, and until next time, enjoy!

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