# What Chords Do You Need?

You famously only need [four chords](https://tvtropes.org/pmwiki/pmwiki.php/Main/TheFourChordsOfPop) to play everything, or maybe it's only [three](https://tvtropes.org/pmwiki/pmwiki.php/Main/ThreeChordsAndTheTruth). But how true is this really?

I decided to go look and see what was common. I looked at a large number of transcribed songs, writing down which chords were used. This isn't perfect: some chords are more optional than others, but it's about right. I only wrote down the triad: C7 and Cmaj7 are just C. I used three sources:

*   [Rise Up Singing](https://en.wikipedia.org/wiki/Rise_Up_Singing): a songbook popular at singalongs. I flipped through and took the chords the 277 songs that seemed most familiar to me.
    
*   [The Portland Collection](https://www.theportlandcollection.com/): a tunebook popular among contra dance musicians. I did the same flipping through, with all three volumes, and took the chords from 89 tunes.
    
*   [Farm and Wilderness](https://en.wikipedia.org/wiki/Farm_%26_Wilderness) String Band Tunebook, Third Edition. All 42 tunes.
    

Out of these 408 songs, here's how many include each chord:

[![](https://www.jefftk.com/tunes-that-use-this-chord-absolute.png)](https://www.jefftk.com/tunes-that-use-this-chord-absolute-big.png)

This isn't a great way to look at it, though, because it is absolute and music is (mostly) relative. We perceive a song that goes "C F G" very similarly to one that goes "A D E". Musicians will often use "Roman Numeral notation" to talk about chords in a purely relative sense. If we look at "C F G" relative to "C", or "A D E" relative to "A", we can call them "I IV V": they are each three major chords using the first, fourth, and fifth notes of the major scale. We indicate minor chords by using a lowercase number: "iv" would be "Am" relative to "C", or "F#m" relative to "A".

Here's what this looks like in C, for example:

| root | major | minor |
| --- | --- | --- |
| C   | I   | i   |
| C#  | bII | bii |
| D   | II  | ii  |
| D#  | bIII | biii |
| E   | III | iii |
| F   | IV  | iv  |
| F#  | bV  | bv  |
| G   | V   | v   |
| Ab  | bVI | bvi |
| A   | VI  | vi  |
| Bb  | bVII | bvii |
| B   | VII | vii |

Here's the same chart as above, but with relative chords:

[![](https://www.jefftk.com/tunes-requiring-chord-unadjusted.png)](https://www.jefftk.com/tunes-requiring-chord-unadjusted-big.png)

This is mechanically converted, and assumes every song is using the standard major scale, which of course they aren't: see all those "i" chords? Instead of thinking of a song with "Am C F G" as being "i bIII bVI bVII", we should think of it as "vi I IV V", as if it is in C (the relative major). This focuses our distribution:

[![](https://www.jefftk.com/tunes-requiring-chord-relative-minor.png)](https://www.jefftk.com/tunes-requiring-chord-relative-minor-big.png)

Some songs are neither major nor minor, but in other modes, typically mixolydian. These have chords like "A G D". Instead of "A G D" being "I bVII IV", we can think of it using the corresponding major and use "V IV I":

[![](https://www.jefftk.com/tunes-requiring-chord-relative-minor-and-mixolydian.png)](https://www.jefftk.com/tunes-requiring-chord-relative-minor-and-mixolydian-big.png)

While it's almost always I, IV, V, and vi, we have both II/ii and III/iii, differing on whether the third is major or minor. One way to handle this is just to drop the third from all the chords and play them open:

[![](https://www.jefftk.com/tunes-requiring-chord-adjusted-open.png)](https://www.jefftk.com/tunes-requiring-chord-adjusted-open-big.png)

So: If we choose a few chords, what fraction of songs/tunes can we play?

| Chords | Thirds | Open |
| --- | --- | --- |
| I IV V | 31% | 31% |
| I iii IV V | 32% | 32% |
| I ii IV V | 39% | 50% |
| I IV V vi | 41% | 41% |
| I iii IV V vi | 45% | 49% |
| I ii IV V vi | 56% | 69% |
| I ii iii IV V vi | 65% | 96% |
| I ii iii III IV V vi | 71% | 96% |
| I ii II iii IV V vi | 82% | 96% |
| I ii II iii III IV V vi | 91% | 96% |

We can actually do slightly better than this: while above I only adjusted for relative minor and mixolydian, we can be more aggressive and try interpreting the song against all 12 possible scale degrees. But it doesn't change things very much:

| Chords | Thirds | Open |
| --- | --- | --- |
| I IV V | 32% | 36% |
| I iii IV V | 33% | 37% |
| I ii IV V | 43% | 57% |
| I IV V vi | 42% | 45% |
| I iii IV V vi | 47% | 54% |
| I ii IV V vi | 60% | 78% |
| I ii iii IV V vi | 68% | 97% |
| I ii iii III IV V vi | 75% | 97% |
| I ii II iii IV V vi | 83% | 97% |
| I ii II iii III IV V vi | 93% | 97% |

There are small differences between songs and contra dance tunes:

|     | Dance Tunes |   | Songs |   |
| --- | --- | --- | --- | --- |
| Chords | Thirds | Open | Thirds | Open |
| I IV V | 21% | 25% | 38% | 42% |
| I iii IV V | 21% | 25% | 38% | 43% |
| I ii IV V | 39% | 56% | 45% | 58% |
| I IV V vi | 35% | 36% | 46% | 49% |
| I iii IV V vi | 44% | 50% | 49% | 55% |
| I ii IV V vi | 65% | 85% | 58% | 75% |
| I ii iii IV V vi | 74% | 99% | 66% | 96% |
| I ii iii III IV V vi | 83% | 99% | 71% | 96% |
| I ii II iii IV V vi | 85% | 99% | 82% | 96% |
| I ii II iii III IV V vi | 98% | 99% | 90% | 96% |

What are those stubborn ones which we still can't play, even with this many chord options?

*   Most common are ones that use multiple keys/modes, especially a switch between major and minor. For example, "Kitchen Girl" needs "A G" for the first half of the tune (confusingly called the "A part") and "Am G E" for the second half.
    
*   Others, like "Be Prepared", use major versions of chords for effect: it uses "C E A D G C" ("I III VI II V I") for a turnaround, following the circle of fifths. You can play it with the minor versions, but it's not as punchy.
    
*   And a few, like "Gee, Officer Krupke", just use a ton of chords in a way I don't really understand.
    

As for how this applies to my own [instrument-making](https://www.jefftk.com/p/foot-chording-chords), for now I've gone with "I ii iii IV V vi" and an option to use open chords.

All code and chords are [on github](https://github.com/jeffkaufman/chords).

*Comment via: [facebook](https://www.facebook.com/jefftk/posts/10100248179972182)*