Analysis of chords of 1300 popular songs for patterns.

Knowing the patterns can give one a deeper more fundamental sense of how music works. This makes listening to music a lot more interesting. If you play an instrument or write songs, being aware of these things is of great practical importance.

In this article, we’ll look at the statistics gathered from 1300 choruses, verses, etc. of popular songs to discover the answer to a few basic questions. First we’ll look at the relative popularity of different chords based on the frequency that they appear in the chord progressions of popular music. Then we’ll begin to look at the relationship that different chords have with one another. For example, if a chord is found in a song, what can we say about the probability for what the next chord will be that comes after it?

The Database

To make quantitative statements about music you need to have data; lots of it. Guitar tab websites have tons of information about the chord progressions that songs use, but the quality is not very high. Just as important, the information is not in a format suitable for gathering statistics. So, over the past 2 years we’ve been slowly and painstakingly building up a database of songs taken mainly from the billboard 100 and analyzing them 1 at a time. At the moment the database of songs has over 1300 entries indexed. The genre and where they are taken from is important. This is an analysis of mainly “popular” music, not jazz or classical, so the results are not meant to be treated as universal. If you’re interested, you can check out the database at http://www.hooktheory.com/analysis/. The entries contain raw information about the chords and melody, while throwing out information about the arrangement and instrumentation.

We can use the information in the song database to answer all sorts of questions. In this introductory post, I’ll look at a few interesting preliminary results, but we invite you to propose your own questions in the comments at the end of the article. Let’s get started.

1. Are some chords more commonly used than others?

This seems like such a basic question, but the answer doesn’t actually tell us much because songs are written in different keys. A song written in C# will have lots of C# chords in it, while a song written in G will probably have lots of G’s. That G chords are more popular than C# chords is likely only a reflection of the fact that it’s easier to play on the guitar and piano. So instead of answering this meaningless question, I’ll answer the slightly more interesting one of, what keys are most popular for the songs in the database?

C (and its relative minor, A) are the most common by far. After that there is a general trend favoring key signatures with less sharps and flats but this is not universal. Eb with 3 flats, for instance, is slightly (though not statistically significantly) more common than F with only 1 flat. Bb only has 2 flats but is way at the end of the popularity scale with only 4% of songs using that as the key.

2. What are the most common chords? Part 2

It’s much more interesting to look at songs written in a single common key. That way direct comparisons are possible and more illuminating. We transposed every song in the database to be in the key of C to make them directly comparable. Then we looked at the number of chord progressions that contained a given chord.

Below we’ve plotted the relative frequency that different chords occurred in descending order.

As expected, C major is a very common chord for songs written in C (it’s the I chord in Roman Numeral or Nashville Number notation), but F major and G major (the IV and V respectively) are used just as often. Interestingly, F and G actually show up in more chord progressions than C! C major is the tonal center and one might expect it to be ubiquitous, but it turns out to be pretty common to omit this chord in some sections of a song for effect. My Heart Will Go On is one of many examples in the database that exhibit this behavior. Clicking on the above link will take you to the song’s entry in the database and show you that of the two sections that were analyzed (the chorus, and the verse), only 1 contains a C.

The A minor chord is the next most popular, but after that there is a significant drop off in use. If you’ve ever heard someone complain about the 4 chord pop song, this is what they are talking about.

Is there a reasonable explanation for the relative popularity of these chords? Why are A minor chords so popular but A major chords practically nonexistent? There won’t always be easy answers, but in this case these results can easily be explained with some basic music theory. A discussion of this is out of the scope of this post, but we’ll definitely explore the Music Theory behind this in future articles.

Even if you don’t know the Music Theory behind this yet, there is a lot of practical information to take away. If your song is written in C and you want it to sound good, you probably shouldn’t use any A major chords unless you really know what you’re doing. Better stick with A minor, for example.

The guys over at Apple, Inc. evidently know their music theory. Their latest version of GarageBand lets you play with “Smart Instruments” that “make you sound like an expert musician… even if you’ve never player a note before.”

I’m skeptical of their claims, but look at the chords they’ve chosen for these “Smart Instruments”:

Don’t those chords look familiar? Based on what our database is showing, I might suggest some small changes.

In particular, Bdim, while diatonic in C, is much less common than some other chords, like D, and E. Perhaps in the next version of garageband, Apple will fix this (they really should).

However, overall Apple is making good choices for the chords that the average “garage band musician” might want to start with.

3. What chord should come next?

The previous question took an overall look at the relative popularity of different chords, but we can also look at the relationship that different chords have to one another. For example, a great question to ask is, if a song happens to use a particular chord, what chord is most likely to come next. Is it random, or will certain chords sound better than others and thus be more likely to show up in the popular songs that make up our database?

There are a lot of relationships to analyze, but we’ll start it off by looking at just one for now: For songs written in C, what chords are most likely to come after an E minor chord?

The relative popularity of what the next chord will be is shown below:

This result is striking. If you write a song in C with an E minor in it, you should probably think very hard if you want to put a chord that is anything other than an A minor chord or an F major chord. For the songs in the database, 93% of the time one of these two chords came next.

Part 2: Analysis of chords of 1300 popular songs for patterns.

This article is Part 2 of a multipart series looking at the statistics gathered from 1300 choruses, verses, etc. of popular songs to discover the answer to some interesting questions about how popular music is structured. Click here to read Part 1.

In Part 1, we used the database to learn what the most frequently occurring chords are in popular music and also started looking at the likelihood that different chords would come after one another in chord progressions.

In Part 2 of this series, we’ll continue this exploration into the patterns evident in the chords and melody of popular music. First we’ll look at how popular music ends musical ideas and discuss a surprising difference between popular music and classical music. Then we’ll talk about the most popular chord progression used by songs in the database and discuss the ubiquity of this progression. Finally we will revisit the question of “which chords occur most frequently in popular music” and look at the reasons for why this is the case.

The first article received A LOT of really great feedback. We’re definitely using the feedback you’re giving to help guide us with where to go next, so keep it coming. Let’s get started with Part 2.

1. What are the most common ways that songs written in C get back to the C major Chord?

For songs written in C major, the C major chord (the I or “one” chord in Roman Numeral notation) is the song’s tonal center, so this is an important question to explore.

Probably the most fundamental rule governing chord progressions in classical music is the idea that in the key of C, G major chords (or V chords) are the right way to wrap up a musical idea. This has been known for ages, and popular music would be expected to do this too. Listen to this section from Aerosmith’s I Don’t Want To Miss A Thing. As the clip plays, we’ve highlighted the chords for you to follow as you listen along.

Listen in particular to that final G chord at the very end of the crazy buildup. That’s a V chord. And that’s how you end chord progressions. That’s just how it’s done.

…Except when it’s not. One of the interesting things about popular music is that this V → I (G to C) resolution isn’t adhered to nearly as much as it is in classical music. How much does popular music depart from this standard? We can answer that by looking at the songs in our database to get a precise answer.

The following plot shows the frequency that the other basic chords are used to come before I (or C major for songs written in C).

What stands out here, is that IV → I (F to C) is not only normal, it actually shows up just as often as V → I. This is surprising (at least to a classically trained person).

We also learn from this data that very few chord progressions go from iii to I (Em to C). In Part 1, we learned that Em (iii) almost always goes to F or Am (IV or vi) so this is totally consistent. Some of you were interested in seeing examples of songs that break with the trends that we’re finding. In that spirit, here’s one song in the database that happens to use Em (iii) in this way: Lady Antebellum’s I Need You Now:

This illustrates the point that it’s definitely possible to “break the rules” and still sound great. If you’re tempted to take this as an invitation to just experiment and do whatever you want, just remember the old mantra that I wish more songwriters would follow: “You’ve got to learn the rules before you can break them”. In fact, in this

very example the weaker iii → I (Em → C) only happens in the first phrase. In the second repetition, the verse is ended much more emphatically with a strong G going to C (V → I). Also notice that the beginning of this section starts on a C (I) chord that is arrived at from an F (IV). So while this song uses the iii in an unusual manner, it is still following a lot of other “rules” elsewhere.

2. What is the most popular chord progression used by songs in our database?

To answer the question many of you were asking in the comments. The most popular 4 chord progression that shows up in the database is in fact the I V vi IV (or C G am F in the key of C). This, by the way, is a great example of a progression that uses the IV instead of V to get back to I. You can listen to a few songs that use this progression below:

What to take away from this? First, let’s be clear that just because a song uses only 4 chords doesn’t mean it’s necessarily stupid or inferior. It’s how you use those 4 chords that counts. Even more importantly though, I want to dispel the notion that popular music can’t be interesting musically.

Even though it’s true that there are a lot of songs that stick to just 4 chords, this definitely isn’t universal. There’s lots of examples in “popular” music that are really rich harmonically.

To give just one example, listen to the chorus from the song Who Says by the John Mayer:

John Mayer songs are often interesting to analyze because he studied at the Berklee School of Music and knows his harmony. This is the type of chord progression that a classical musician would recognize and understand immediately.

But popular music also uses chords in ways that are different from what a purely classically trained musician would be accustomed to hearing. Consider Christina Aguilera’s I Turn To You:

There’s obviously a lot going on in this song harmonically, and while I’m sure you guys will analyze every detail in the comments, the point I’m trying to make here is that there are examples of interesting uses of chords in popular music everywhere. You just have to look for it.

3. “Why” are the most frequently used chords in popular music what they are?

In part I, we found out that the most commonly occurring chords were the following:

The reality is, and this was pointed out by many of you in the comments, that a lot of the explanation behind all of this can be answered with some basic music theory. If you’re interested in learning some of the reasons that these chords are popular, we encourage you to check out our interactive book , that teaches the theory behind popular music in ways that are approachable and fun to all musicians. Thanks for reading! Let us know what you think in the comments below. http://www.hooktheory.com/music-theory-for-songwriting

A statistical study of inversions (slash chords) in popular music.

This article is Part 3 of a multipart series looking at the statistics gathered from 1300 choruses, verses, etc. of popular songs to discover the answer to some interesting questions about how popular music is structured.

In this article, we’ll continue our exploration into the patterns evident in the chords and melody of popular music. First we will look at the relative popularity of different inversions (e.g. a C/E chord vs. G/B, etc.) based on the frequency that they appear in chord progressions found in the Hooktheory Analysis Database. Then we will take a statistical look at how inversions are most often used. For example, if an inverted chord is found in a song, what can we say about the probability for what the next chord will be that comes after it? This will be compared with how the non-inverted counterpart of the chord is used (e.g. a C/E vs. a C).

Inverted Chords

When a song is using a C major chord, the lowest note (often played by the bass player if there is one) is usually a C. Sometimes this is not the case, however, and one of the other notes that make up the C major chord will be played instead (the E, or G). These so-called inverted chords occur frequently in popular music. Guitarists reading tablature will recognize them as “slash chords” (i.e. C/E) where the note below the slash is the new bass note.

The Popularity of inversions of C and G

Any chord can be inverted, but in practice it turns out only a few are commonly used in popular music. Amongst songs that had inversions in them, the following plot shows the rate at which different inverted chords show up in the database. All songs were transposed to the key of C to make comparison between songs in different keys valid.

The plot shows that C/E and G/B chords (I6 and V6 in Roman Numeral notation) are the most common by far. Part of this can be explained by the fact that, as we learned in Part 1, I and V chords are very popular chords in general. Yet we also learned that IV and vi chords are almost as popular, and inversions of these chords show up much less frequently than you might expect.

Perhaps a more interesting question to ask is, given that C/E and G/B (I6 and V6) are so popular, how are these chords used relative to their non-inverted vanilla C and G chords? In other words, how does changing the bass note of the chord change how the chord functions?

This question is readily answerable with empirical data from the Hooktheory database.

The usage of C/E vs. C

Let’s start by comparing C/E and C. The following plot below shows the probabilities for what the next chord in the chord progression will be after each chord. The first plot shows the probability for the chord coming after a vanilla C (I) chord. The second plot shows how the probability changes when this chord is instead a C/E (I6) chord.

The most common chords to follow a vanilla C (I) chord are unsurprisingly G (V) and F (IV) (occurring 26% and 46% of the time respectively). The tendencies change dramatically for C/E, however, with F (IV) being by far the most common chord and Dm (ii) gaining quite a bit of ground. Dm is almost 3 times more likely to come after a C/E chord as compared to a vanilla C chord (23% vs. 8%).

These statistics reveal an important function of inverted chords. Inversions are often used to link the bass notes between neighboring chords. In this case the E in the bass of C/E is a neighbor to the D and F in the bass of Dm and F respectively. This is very much in line with what a classically trained musician would expect, but it’s interesting to see these chords used in this way given that many popular songs are composed by people without classical backgrounds. The reason this is such a powerful technique is that our ears hear the lowest note in a song very strongly. It is perhaps less strong than the top note which is why melodies are so important, but the bass note is definitely critical (bass players can take solace in this fact).

A great example of a song that uses the I6 in this way is the intro of Michael Jackson’s Man in the Mirror. The song floats between ii (Dm) and IV (F) using I6 before finishing in textbook fashion with IV → V → I.

The usage of G/B vs. G

We find a similar story for G/B (V6). The following plot shows the probabilities for what the next chord in the chord progression will be after each chord. As before, the first plot shows the probability for the chord coming after a vanilla G (V) chord. The second plot shows how the probability changes when this chord is instead a G/B (V6) chord.

The plot shows that vanilla G (V) chords normally split almost evenly between going to C, F, and Am (I, IV, vi) (32%, 25%, and 29% respectively). Again since these are the most common chords, this should be not be all that surprising. However, the data clearly show that this is no longer the case for G/B (V6). Going to the vi doubles in popularity (from 29% to 61%) to become far and away the most popular transition. F (IV) takes a big hit, occurring 2.5 times less frequently, while C (I) holds more or less steady. Why does G/B to Am seem to occur so much more than G to Am? It’s likely for the same reason that C/E likes to go to F and D so much. Linking up neighboring bass notes creates a nice effect that clearly is a very common technique in popular music.

A good example of a song in the database that uses G/B like this is the Rolling Stone’s “Beast of Burden”:

Here are some other examples in the Song Database that do this too:“Freebird” by Lynard Skynard“You’re Beautiful” by James Blunt

“Your Song” by Elton John is a song that does something uncommon after G/B. It goes to the iii (Em). Aside from this departure, Elton tends to use chords in a very typical fashion (though he’s uses every trick in the book to get the sound he wants).

Though he doesn’t use the V6 to create a linked bass line here, he uses inversions of 7 chords (vi42) and secondary dominants (vii˚7/V, oh my!) to connect the vanilla vi chord by step with the IV to complete the progression (the bass note goes A → G → F# → F. We’ll talk about how songwriters like Elton use these more complex harmonies in future posts.

What’s your favorite use of inverted chords in a pop song? Are they used in a way consistent with these findings? Let us know in the comments below.