Understanding the mood of the bass line and harmony

In this lesson we will look at how the bass line and harmony for a song can create the mood. For this, you need to know what a chord is and how a bass line and harmony is created from chords. If you don’t know that, check out my lesson Composing a bass line and harmony for Happy Birthday and then come back here.

As you know, a bass line is composed of chords, usually played in a repeating pattern. In this lesson we will look at how the chords chosen affect the mood of the song. 

What is a chord progression?

When creating a bass line, if you were to play the C chord, then the G chord, then the C chord again and then the G chord again, this would be a chord progression of C-G-C-G. If each chord is used for an entire bar, this progression would play for four bars. 

In a song, the composer usually creates a chord progression that has repeating elements, rather than randomly picking an individual chord for each bar. For example, a song might be created by choosing an 8 bar chord progression that repeats from start to finish.  Or an 8 bar chord progression might be played twice in a row for each verse, then the chorus might be created using a different 8 bar chord progression.

The chord progression can be used to tell a story through music. Each chord can be used to set a different scene.

How are chord progressions described?

We have already learnt that a chord can be created from the 1, 3 and 5 notes of the scale, counting from the root note of the chord, and that by describing the chord with numbers, we know how to create any chord in any key. In the same way, it is valuable to describe chord progressions using numbers, so that a chord progression can be applied to any key. We used Arabic numbers (1, 2, 3 etc) to describe the notes of the chord. To avoid confusing the notes of the chord with chord progressions, chord progressions are described using Roman numerals.

Here are the Roman numerals you need to know, along with their equivalent Arabic numbers:

You will notice that some of the Roman numerals are capital and some are lower case, and that there is a little ‘º’ after the ‘vii.’ For now, ignore these – we’ll come back to what these mean a bit later.

See how the Roman numerals describe the C Major scale:

As you can see, each note of the scale has an equivalent Roman numeral. Remember the chord progression I described above, C-G-C-G? We could describe that using Roman numerals, which would be I-V-I-V.

Can you work out how to describe the chord progression C-F-G-C of the C Major scale using Roman numerals? See the end of this lesson for the answer.

Now look at the G major scale:

What chords would we play if we want to apply the progression I-V-I-V?

What chords would we play in the G major scale for the progression I-V-VI-IV?

See the end of this lesson for answers.

Knowing the difference between major and minor chords

Just as the key for a song can be major or minor, so can chords. Even when a scale is major, some of the chords for that scale are minor. Minor chords are written using lower case Roman numerals. Choosing to include a minor chord in the progression for a song in a major key can introduce wistfulness, longing, sadness and other emotions. Some chords are considered ‘diminished’, which give them a tense, dark, unstable energy. For a diminished chord, it is written with lower case Roman numerals, and we add the symbol ‘º’ immediately after it.

For a major scale, some chords are inherently minor, and the seventh chord is inherently diminished.

The following list shows which chords are major, which are minor, and which are diminished for a major scale:

  • I 1st chord: major
  • ii 2nd chord: minor
  • iii 3rd chord: minor
  • IV 4th chord: major
  • V 5th chord: major
  • vi 6th chord: minor
  • viiº 7th chord: diminished

When a chord progression is written using the correct mix of upper case and lower case Roman numerals, you can see immediately the extent to which it can be considered bright and happy, versus sad, melancholic or tense.

If we go back to the last chord progression I described above, I-V-VI-IV, the correct way to write it is I-V-vi-IV, because in a major key the 6th chord is a minor chord so needs to be written with lower case letters.

Writing chord progressions for minor keys

For every major key, there is a relative minor key. For the key of C major, its relative is A minor. Exactly the same notes are present in both the major and minor key, but for C major we would write them as:

C – D – E – F – G – A – B

and for A minor we would write them as:

A – B – C – D – E – F – G

The difference is that in A minor, ‘A’ is the home chord, whereas in C major, ‘C’ is the home chord.

When people write down the Roman numerals for the chord progressions of songs written in minor keys, it can become a bit confusing, because there are two ways to do it. The first method, written as major, is the one I will use in this course. It uses the same notation as we use for major keys:

See how the song in the minor key starts with the vi chord? For a song in A minor, the progression vi IV I V (six, four, one, five) written this way would be A – F – A – G. This is one of the most popular chord progressions for minor songs in Western music.

What would be the chords for the progression vi V IV in a minor song? See the end of the lesson for the answer.

The second method for describing the chord progression of a song in a minor key, written as minor, involves changing the Roman numbering so that it starts with A as the first chord, therefore giving it the Roman numeral ‘i’. (It is written as a lower case ‘i’, not upper case ‘I’, because the first chord is a minor chord.) When we adjust the chord progression to be written as minor, the chords would be written with the following notation:

We can still see which ones are major chords and which are minor chords and which is diminished, from seeing whether the Roman numerals are written with upper case letters, lower case letters, and with or without the ‘º’ symbol.

In a chord progression written as minor, the chords are:

  • i 1st chord: minor
  • iiº 2nd chord: diminished
  • III 3rd chord: major
  • iv 4th chord: minor
  • v 5th chord: minor
  • VI 6th chord: major
  • VII 7th chord: major

How a chord progression tells a story

Think of each chord as setting a different scene in a story. The first chord, the I chord in a major key, is like home base. Chord progressions often start with the I chord (home) and then head off to other places. If you wrote a piece of music that uses only the I chord, it would be like telling the story, ‘I stayed home, it was nice, but I didn’t go anywhere.’ It could sound lovely if you create an interesting rhythm with the bass line and write a pretty melody, but it won’t feel like it’s going anywhere. 

If we start on the I chord, then go to the V chord, then repeat this 2-chord progression, it would be like saying ‘I was at home and it was nice (I), then I left to explore on a happy adventure (V), then I came home again which was also nice (I), then I went out again… The chord progression would be I-V-I-V. This is a very simple story, but it’s one that goes somewhere, and, importantly, returns.

Most stories become interesting when some tension or challenge or difficulty is introduced, and this can be achieved in music by using a minor or diminished chord.

The most common chord progression in Western music is I-V-vi-IV. If you were to speak this aloud, you would say, ‘one, five, six, four.’ You can think of it as starting at home (I), going out for a happy exploration (V), encountering some sadness (vi), then finding a silver lining in the sadness (IV).

When the chord progression is repeated, the I at the start of the repeat creates the feeling of returning home. At the very end of the song, if there are no more repeats, you can add an extra bar with the I chord, to return home.

This chord progression is often used to create emotionally tender songs, or songs that are sweet and a bit melancholic. It sounds natural and familiar, is catchy and can support very beautiful melodies. It is so effective that it has been used many times.

If you return to the cooking analogy we have talked about in this course, you can think of this chord progression as being like cheesecake – it’s sweet and satisfying, and it’s a very standard dessert offering. Think of the vi chord as like a tart berry on top of the cheesecake, providing contrast that goes well with the sweetness, which could otherwise be a bit sickly.

If you were in a band and discussing which chord progression to use, for this one you would simply suggest trying a ‘one, five, six, four’ chord.

These four chords, I, V, vi, and IV, are the most popular chords used in Western songs, and they can be reorganised to achieve a variety of effects:

I-vi-V-IV (one, six, five, four). Starting at home with a major chord (I) gives a sense of optimism, which quickly falls to the sombre vi chord, then rises again to give a feeling of enduring optimism (V-IV).

vi IV I V (six, four, one, five). This starts on the vi chord instead of the I, and causes the vi chord to feel like the ‘home’ chord of the progression. Since the home chord is a minor chord, it is like the home is imbued with sadness and is less optimistic than the previous progressions described.

vi V IV V (six, five, four, five). Once again, this has the sad feeling overall, but going down through V-IV, then up again to V-vi, creates the feeling of an epic, valiant, romantic struggle.

I IV vi V (one, four, six, five). This one feels more optimistic. It’s the equivalent of someone sitting in an old rocking chair telling a story along the lines of, ‘Ahhh, those were the days.’ It’s sweet and nostalgic but there is also some sadness that the days are past. 

The four chords used here can be arranged in just about any order to good effect, but the above examples are tried and true formulas that have been used to make hundreds of thousands of popular songs across many genres, including pop, folk, rock and country.

In general, if a song is in a major key, it will start on the I chord for that scale. If it is in a minor key, it will start on the vi chord (though it might be described as starting on the i chord).

Answers to the questions above

  • The chord progression C-F-G-C of the C Major scale using Roman numerals is I-IV-V-I.
  • The progression I-V-I-V in G major is G-D-G-D.
  • The progression I-vi-I-V in G major is G-D-E-C.
  • The chords for the progression vi V IV in a minor song are A G F.

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