What Are Perfect Intervals?, Learn how to recognize and build the 3 different Perfect Intervals
Mar 16 2013, 10:20 AM
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What Are Perfect Intervals?

In this Theory lesson we’ll be looking at one of the most commonly used intervals in modern music, the Perfect Interval.

There are 3 different Perfect Intervals in music, the Perfect 4th, Perfect 5th and Perfect Unison/Octave.

Each of these intervals can be found in the major scale, and so if you know your major scale notes you can always find these intervals from any given root as they will be the intervals found in that scale.

For example, if you have a C major scale:

C D E F G A B C

And you want to find the Perfect Intervals, you simply look at the 1st, 4th, 5th and 8th notes of that scale.

C-F = Perfect 4th
C-G = Perfect 5th
C-C = Perfect Octave/Unison

For those of us that are still learning the notes of our major scales, there are formulas that you can memorize and use to figure out all of these intervals without knowing the notes of their corresponding major scales.

Here are those formulas to check out.

Perfect 4th Intervals

There are two ways that you can find Perfect 4th intervals, one on the guitar and one using whole-steps to build this interval.

On the guitar, if you have a starting note, say G, and you are on the 6th, 5th, 4th or 2nd string, you simply go one string higher, staying on the same fret, and you have a Perfect 4th interval, C in this case.

If you are on the 3rd string, you need to go 1 string up and 1 fret forward, since the 2nd string is tuned differently from the rest, to find a Perfect 4th interval.

To build a Perfect 4th from an interval standpoint, you start on your root note, G for example, and then you move up 2.5 whole-steps, G-A-B-C, to find your note, again C in this instance.

Here are a couple of examples of Perfect 4th intervals written out on different parts of the neck.

After you’ve learned how to build a Perfect 4th interval, go ahead and write a number of them out and post your work below. I will be happy to go over and check your work to make sure that you’re on the right track when it comes to identifying and writing this interval.

Perfect 5th Intervals

Similarly, there are two ways you can find a Perfect 5th interval above a note, one on the guitar and one off the guitar.

On the guitar, if you have a root note on the 6th, 5th, 4th or 2nd string, you simply move up 1 string and forward 2 frets and you have a Perfect 5th interval, creating the “Power Chord” shape that we all know and love.

For the 3rd-string root note, you go up 1 string and forward 3 frets to find a Perfect 5th, again due to the tuning of that string being different from the others.

Off the guitar, you can move up 3.5 whole steps from your root-note to find a Perfect 5th interval, such as moving from G to D, G-A-B-C#-D, to make a Perfect 5th above G.

Here are a couple of examples of Perfect 5th intervals written out on different parts of the neck.

After you’ve learned how to build a Perfect 5th interval, go ahead and write a number of them out and post your work below. I will be happy to go over and check your work to make sure that you’re on the right track when it comes to identifying and writing this interval.

Unison and Octave Intervals

The last Perfect interval has two sides to it’s construction.

The Perfect Unison is built by playing the same note in the same range, so to G’s that sound the exact same, but that may or may not be played on the same string as you can see in the example below.

A Perfect Octave interval is the same note, such as E and E, but that are separated by the musical alphabet on the staff, so they sound in different ranges of the instrument such as in the example below.

Here are a couple of examples of Unison and Octave intervals written out on different parts of the neck.

After you’ve learned how to build Unison and Octave intervals, go ahead and write a number of them out and post your work below. I will be happy to go over and check your work to make sure that you’re on the right track when it comes to identifying and writing this interval.

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This post has been edited by The Professor: Mar 18 2013, 11:48 AM

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Mar 16 2013, 05:29 PM
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i always wondered why are they called "perfect"?

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Mar 16 2013, 09:56 PM
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I think its something to do with the fact that if you flipped them, then they stay 5ths, etc etc.
where as if you took for example the notes : G to E (which is a major 6th) and flipped them, you would have E to G, which becomes a minor 3rd.

QUOTE (MonkeyDAthos @ Mar 16 2013, 04:29 PM)
i always wondered why are they called "perfect"?

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Mar 17 2013, 01:12 AM
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QUOTE (MonkeyDAthos @ Mar 16 2013, 04:29 PM)
i always wondered why are they called "perfect"?

This term goes way back as these intervals, unison-octave-4th-5th are considered "perfectly" consonant. Basically very stable as opposed to the other intervals, major or minor etc, which are less stable.

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Mar 18 2013, 10:49 AM
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QUOTE (The Professor @ Mar 17 2013, 01:12 AM)
This term goes way back as these intervals, unison-octave-4th-5th are considered "perfectly" consonant. Basically very stable as opposed to the other intervals, major or minor etc, which are less stable.

So basically stable intervals are 100% non-dissonant (=consonant), whereas a minor third could be described as slightly dissonant (for lack of a better word).

If students want to try this out they could hit a two note chord and hear the difference. Here is a perfect interval (a fifth):

`-------------------------7-----------5----------------------`

You can hear this chord is happy with its own existence and wants to go nowhere.

However, here is a "less stable" interval (minor third):

`-------------------------3-----------5----------------------`

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Would this be an accurate way of describing it?

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Mar 18 2013, 11:30 AM
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QUOTE (Kristofer Dahl @ Mar 18 2013, 09:49 AM)
So basically stable intervals are 100% non-dissonant (=consonant), whereas a minor third could be described as slightly dissonant (in lack of a better word).

If students want to try this out they could hit a two note chord and hear the difference. Here is a perfect interval (a fifth):

`-------------------------7-----------5----------------------`

You can hear this chord is happy with its own existence and wants to go nowhere.

However, here is a "less stable" interval (minor third):

`-------------------------3-----------5----------------------`

----

Would this be an accurate way of describing it?

That's a good way to think about it. It may seem a bit funny in modern times, but basically any interval that isn't perfect was once considered at least slightly dissonant. But, maybe a better word for us to use nowadays is "stable."

So, Major, Minor, Diminished and Augmented intervals want to move somewhere, they don't sound like they are "finished" right there. Whereas Perfect intervals sound like you've arrived somewhere, like they are stable and secure.

Might be a better way to think of it as in today's world we don't think a minor 3rd is dissonant anymore, whereas hundreds of years ago when they came up with these terms that was a freaky interval! lol

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