Perfect Intervals

An Essential Guide To Unisons, Perfect Fourths, Perfect Fifths and Octaves

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Perfect intervals are considered as perfectly consonant.

Perfect Intervals

Consonance is a perception of unity or tonal fusion between two notes. If an interval is consonant, then we perceive it as blended and stable. The upper notes of perfect intervals are within the major scale built on the lower note. Let’s have a look at an example with all perfect intervals starting with the note C in harmonic form.

Perfect Intervals
Perfect Intervals

We use an uppercase P with its quantity to indicate a perfect interval. All unisons (P1), all octaves (P8) are perfect. Also, most fourths and fifths except augmented fourths (A4) and diminished fifths (d5) are also perfect. (P4 and P5). Here is a table showing which perfect intervals have how many half steps.

INTERVAL NAME

SYMBOL

NUMBER OF HALF STEPS

Perfect Unison

P1

0

Perfect Fourth

P4

5

Perfect Fifth

P5

7

Perfect Octave

P8

12

Unison

As I mentioned before in my interval article, when two tones sounding the same pitch, usually at the same time,  we call this interval unison or perfect unison or prime. Both notes should have the same name. If we want to indicate a unison which consists of accidental notes, we place only one accidental sign before the notes.

E-E Unison
E-E Unison

Note that, E-E interval is not the same as E-F flat. E-E is a unison, while E-F flat is a diminished second. Although they sound like they indicate the same interval, unisons always have same note names. But E-F flat is a second interval. Because they have two different note names. Let’s have a look at all unisons that we can build now.

All Unisons

In this figure, you can see some unison intervals starting on all notes including enharmonic equivalents. Notice that these are harmonic intervals.

Perfect Fourth Interval

Within a perfect fourth interval, there are four note names and the notes are five half steps away from each other. Let’s see an example.

Ascending Perfect Fourth Interval

F-B Flat Perfect Fourth Interval
F-B Flat Perfect Fourth Interval

In this figure, you can see F-B flat ascending melodic perfect fourth interval. It is ascending because it starts with a low pitch note and ends with a high pitch note. Between F and B flat there are four notes: F, G, A, and B. But B is flat. Now let’s look at the quality of his interval. There are five half steps within this interval: F-F sharp, F sharp-G, G-G sharp, G sharp-A, A-A sharp or in this case its enharmonic equivalent B flat. The best way to recognize intervals is to associate them with some reference songs you know well. For an ascending perfect fourth, the best reference song is Amazing Grace. The interval between the notes that correspond to A-ma of Amazing is a perfect fourth. Let’s see this perfect fourth on a piano keyboard now.

F-B Flat Perfect Fourth Interval
F-B Flat Perfect Fourth Interval On A Piano Keyboard

Now let’s look at a descending perfect fourth interval.

Descending Perfect Fourth Interval

C-G Perfect Fourth Interval
C-G Perfect Fourth Interval

In this figure, you can see that the first note C is higher than the second note G in pitch. So this is a descending interval. It is melodic because these two notes sound successive. From C to G there are four notes while descending:C, B, A, and G. Because it is a descending interval, we think of the note names in reverse. There are five half steps between C to G while descending:C-B, B-B flat, B flat-A, A-A flat, and A flat-G. Let’s have a look at this interval on a piano keyboard now.

C-G Perfect Fourth Interval
C-G Perfect Fourth Interval On A Piano Keyboard

One of the best reference work that you can distinguish a descending perfect fourth is the first movement (Allegro) of A Little Night Music of Wolfgang Amadeus Mozart. The intervals between the first three notes of this work are a descending perfect fourth and an ascending perfect fourth. There are 42 perfect fourth intervals ascending and descending that we can write by starting on different notes.

Now let’s have a look at all these perfect fourths both ascending and descending, starting on all notes.

All Perfect Fourth Intervals

All Perfect Fourth Intervals

Notice that some of the notes can have double sharps or double flats just to build the interval. You don’t have to memorize them all. Just know that there are five half steps between them.

Perfect Fifth Interval

Within a perfect fifth interval, there are five note names and the notes are seven half steps away from each other. Let’s see an example.

C-G Perfect Fifth Interval
C-G Perfect Fifth Interval

In this example, there are two measures. The first one has two half notes. You can see an ascending melodic fifth interval between C and G. The second one has two whole notes. You can see a harmonic perfect fifth interval between the same notes. Between C and G, there are five notes:C, D, E, and G. Within this perfect fifth, there are seven half steps:C-C sharp, C sharp-D, D-D sharp, D sharp-E, E-F, F-F sharp, and F sharp-G. For an ascending perfect fifth, the best reference song is Twinkle Twinkle Little Star. Between the words Twinkle and Twinkle, an ascending perfect fifth interval occurs.

Let’s see this interval on a piano keyboard now.

C-G Perfect Fifth Interval
C-G Perfect Fifth Interval On A Piano Keyboard

Notice that if you go from a lower C to higher G, an ascending perfect fifth occurs. But if you go from a higher C to a lower G, a descending perfect fourth interval occurs. It is all about the inversion of intervals which you’ll learn about later. Now let’s have a look at a descending perfect fifth interval example.

Descending Perfect Fifth Interval

D-G Perfect Fifth Interval
D-G Perfect Fifth Interval

In this example, there are two measures again. The first one has a descending melodic perfect fifth from D to G. The second one has a harmonic perfect fifth between the same notes. Between D and G, there are five notes: D, C, B, A, and G. Within this perfect fifth, there are seven half steps again:D-D flat, D flat-C, C-B, B-B flat, B flat-A, A-A flat, and A flat-G. For a descending perfect fifth, one of the best reference songs is Feelings by Richard Clayderman. The main melody of this song starts with a descending perfect fifth interval.

Let’s see this interval on a piano keyboard now.

D-G Perfect Fifth Interval
D-G Perfect Fifth Interval On A Piano Keyboard

Notice that if you go from a higher D to lower G, a descending perfect fifth interval occurs. But if you go from a lower D to a higher G, an ascending perfect fourth interval occurs. Now let’s have a look at all perfect fifths starting on all notes both ascending and descending.

All Perfect Fifth Intervals

All Perfect Fifth Intervals

As you can see, there are 42 perfect fifth intervals ascending and descending that we can write by starting on different notes. Notice that some of the notes can have double sharps, double flats or naturals just to build the interval. There are seven half steps within each of these intervals.

Octave

The last but not least of perfect intervals are octaves. Within an octave or perfect octave, there are eight note names. Seven of them have different names. The eighth one has the same name with the root note. The notes of this interval are twelve half steps away from each other. Finding an octave is easy because the two notes of the interval have the same names but different pitches. Let’s see an example.

Ascending Octave

E-E Octave
E-E Octave

In this example, you can see an ascending melodic octave and a harmonic octave of E. Within this octave, there are twelve half steps: E-F, F-F sharp, F sharp-G, G-G sharp, G sharp-A, A-A sharp, A sharp-B, B-C, C-C sharp, C sharp-D, D-D sharp, and D sharp-E. Now let’s have a look at a descending one.

Descending Octave

F-F Octave
F-F Octave

In this example, you can see a descending melodic octave and a harmonic octave of F. The half steps within this octave are F-E, E-E flat, E flat-D, D-D flat, D flat-C, C-B, B-B flat, B flat-A, A-A flat, A flat-G, G-G flat, G flat-F. So there are twelve half steps again. Now let’s see all octaves starting on all notes in melodic form.

All octaves

All octaves

In these figures, you can see melodic octaves starting on different notes both ascending and descending, including enharmonic equivalents. We can write more octaves with ledger lines and even different parts with different clefs. But they will have basically the same note names with these.

 

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