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Music theory II - Intervals

This is part two of the music theory course. In this second part I assume that you went through the first part. The first course was about scales, this second part is about intervals. You need to know about scales to fully understand intervals.

Why learn about intervals?

Like everything in music theory, some knowledge helps you to communicate about music. If you know the right words and terms, it is easier to communicate with fellow musicians.
A more important reason to learn about intervals is ear-training. If you know intervals, you can start recognizing them in music, which will train your musical hearing.
Yet another reason is that melodies are formed using intervals. If you know your intervals, you will be able to form better melodies.
Finaly, the probably most important reason for learning intervals is the fact that they will give you essential information that is needed to understand chords.
So there is reason enough to dive into intervals, let's start!

What is an interval?

An interval is the distance between two tones.

When we talked about scales in part I of this course, we saw that scales are built using whole or semitones. Whole and semitones are intervals: distances between tones.
Also, we looked at the third tone in scales. We saw that if the distance between the first and third tone is "large", the scale is a major scale. If the distance is smaller, the scale is a minor scale. Exactly! The interval differs! Major has a large third, minor has a small third.

Melodic and harmonic

An interval can be "melodic". In that case the two tones are played in sequence, as in a melody.
Or an interval can be "harmonic". In that case the two tones are played at the same time.

Types of intervals

There are just as many intervals as possible distances between tones. In this course - and in the normal life of a musician, it is sufficient to know the intervals that are smaller than two octaves.

An important concept of intervals, is that they are based on the tones of a scale.

A scale has seven tones. If we add the root tone at the end, there are eight tones. For example the scale of C major (the easy one):

Just as the number of tones, there are eight intervals in this scale:

• From C to C (itself!) is called an "unison"
• From C to D is called a "second"
• From C to E is called a "third"
• From C to F is called a "fourth"
• From C to G is called a "fifth"
• From C to A is called a "sixth"
• From C to B is called a "seventh"
• From C to the other C is called an "octave"

This looks pretty straight forward and it is! However, to really understand intervals, you'll need the same "mindset" as with scales. It is all about the letters:

• If the distance between the letters is zero, the name of the interval is "unison"
• If the tones are just one letter apart (C-D), the name is "second". So also D-E is a "second". And B to C is a second, and G to A. All "seconds"
• If the tones are two letters apart (C-E), the name is "third". If you start counting at 1, then C=1, D=2, E=3, so C-E is a "third". D-F is also a "third": D=1, E=2, F=3.
  As you know, after G we go back to A again. So F-A is also a "third": F=1, G=2, A=3
• If the tones are three letters apart (C-F), the name is "fourth": C=1,D=2,E=3,F=4. Or as example: G-C is a "fourth": G=1, A=2, B=3, C=4. Do you see the pattern?
• If the tones are four letters apart (C-G), the name is "fifth". C=1, D=2, E=3, F=4, G=5
• If the tones are five letters apart (C-A), the name i "sixth"
• If the tones are six letters apart (C-B), the name i "seventh"
• If the tones are seven letters apart (C-other C), the name is "octave"

However this is not the full story!

Let's take a look at two scales: the scale of C and the scale of C minor:

The distance between C and E is two letters.
The distance between C and Eb is also two letters.
What we know now, is that both C-E and C-Eb are "thirds". That is correct.
They are both thirds, but they sound differently. The actual distance between the tones is different.
The actual distance in tones between C and E is two whole tones.
The actual distance in tones between C and Eb is one and a half tone.

So compared to each other, the distance between C and E is larger, the distance between C and Eb is smaller.
In music the proper word for large is "major", the word for small is "minor".
So C-E and C-Eb are both thirds, but different kind of thirds.

C-E is a major third
C-Eb is a minor third

Apart from major and minor, intervals can also be "perfect", "augmented" or "diminished".
In the following we will look at all intervals separately, and investigate this major, minor, perfect, augmented and diminished system.

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