4.8 Perfect fourth and octave
Category: Harmony  Tags: Intervals, Ear training: intervals 
Theory
In Chapter 1.11 Second, third, fourth and fifth you’ve learned what a fourth is. In this chapter, you will learn about the perfect fourth and octave. You also learn about the unison. In the videos and examples I show how to make perfect fourths and octaves. You learn to recognize perfect fourths and octaves and you are goning to make them yourself in the exercises. You will also learn to distinguish perfect fourths, fifths and octaves by ear.
1. What is a perfect fourth?
The fourth C F is made up of two whole steps and one half step.
A fourth made up of two whole steps and one half step is called a perfect fourth.
There is no major or minor fourth. The 'Ding, ding, dong' of the chlidren's song Brother John (Frère Jacques) is a perfect fourth.
The perfect fourth C F.
Video
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Examples
How is a perfect fourth build?
2. Perfect fourths
Video
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Examples
Which tones do you get if you make perfect fourths on the natural notes?
3. What is a perfect octave?
The octave C C is made up of two tones of the same name.
An octave made up of two tones of the same name is called a perfect octave.
There is no major or minor octave. The perfect octave always sounds very consonant.
The perfect octave C C.
Video
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Examples
Which tones do you get if you make perfect octaves on the natural notes?
4. What is a unison?
A unison is an interval of 1 step and consists of two identical natural notes. For example, the interval between the C and itself is a unison, but also the interval between C and Csharp. An interval of two (exactly) the same notes is called a perfect unison. Examples are: G G, G# G#, C C. For pianists it is difficult to imagine that a perfect unison is an interval. After all, on the piano you only play one key and that's not an interval, right? But consider that a perfect unison can be played by two different instruments, for example a violin and clarinet, then it is clear that it does involve two different notes and that a perfect prime is an interval.
Examples
How is a unison build?
5. Practise
Harmony exercise 4a: practise recognizing perfect fourths, fifths and octaves from musical notation.
Harmony exercise 4b: practise making perfect fourths on the natural notes.
Harmony exercise 4c: practise making perfect fourths on all notes.
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Practise
Ear Training exercise 4f: practise distinguishing the difference between a perfect fourth, fifth and octave by ear.
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Which interval do you hear?
Choise 1: perfect fourth
Choise 2: perfect fifth
Choise 3: perfect octave
Practical steps
Sing the interval being played to train your inner hearing abilties. Decide which interval is being played.
Answer: perfect fifth.
Summary
Perfect fourth and octave
 The distance of C to F is called a perfect fourth
 The distance of C to C is called a perfect octave
 There is no major or minor fourth
 There is no major or minor octave
Perfect fourth on the natural notes 

natural note  perfect fourth 
A  A D 
B  B E 
C  C F 
D  D G 
E  E A 
F  F Bb 
G  G C 
Perfect octave on the natural notes 

natural note  perfect octave 
A  A A 
B  B B 
C  C C 
D  D D 
E  E E 
F  F F 
G  G G 
Practise
Harmony exercise 4a: practise recognizing perfect fourths, fifths and octaves from musical notation.
Harmony exercise 4b: practise making perfect fourths on the natural notes.
Harmony exercise 4c: practise making perfect fourths on all notes.
Get the full courseEar training
Ear Training exercise 4f: practise distinguishing the difference between a perfect fourth, fifth and octave by ear.
Get the full course