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So music has a popular set of chords that appears very often: I IV V vi. It's the primary triads + 6th chord, which is also the relative minor. Of all the chords I find that these are the most popular and appear in the most songs, especially the ones that top the charts.

I was watching this great busker which made me think about it. Most buskers play I IV V vi songs again and again because it is what gets the audience most excited. Here's the chords to a few of those songs. Ed Sheeran also mentioned this in an interview, "You name any song and I'll play them in 4 chords". Same was shown by axis of awesome.

But I was just wondering what it is about these chords that people are so drawn to them that they appear again and again? They seem to make hit songs.

  • blah, I just noticed I asked a similar question in the past. I completely forgot about it. music.stackexchange.com/questions/82507/… – user34288 Apr 8 at 6:15
  • Similar, but certainly not the same - that question is only about one chord, whereas this is about the relationships between four chords. Additionally, that question got closed as being opinon-based, whereas by pointing out this you've shown some evidence for this one. – topo Reinstate Monica Apr 8 at 6:28
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    BTW the axis of awesome track shows something more specific than "You name any song and I'll play them in 4 chords" - it features a bunch of songs that actually have the same particular chord progression. – topo Reinstate Monica Apr 8 at 6:30
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    @topo The analogy tries to hint that the things that are used for maximizing sales in mass-marketing might tell something about the target audience and their cultural background, not necessarily about the things themselves. Go to India in the year 1900. Which chords are used the most? Oh, they're not really using chords at all, they're playing drones ... Ok, so what is it about drones that makes them produce all the hits? (naturally forgetting to add ... "for this audience, in this culture, during this period of time in history", because such details would reduce attention value?) – piiperi Reinstate Monica Apr 8 at 8:28
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    If the question was properly narrowed down to a particular culture and time period, then it would be more about that culture than chords. Why do people like to hear familiar sounds? Why do Americans want to listen to whatever they speculate is common? (I read that Americans are highly intolerant of hearing any music that doesn't feel mainstream, so they immediately switch the radio station if there's any hint of something weird or foreign or different) – piiperi Reinstate Monica Apr 8 at 9:08
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I would disagree in that first, if 1 4 5 6 are the rule, then there are lots of very effective and widely used exceptions to the rule. Secondly, I think all of the first six diatonic chords are equally important and used. The vii dim is rarely used.

It all comes down to diatonic harmonic function. Classical music theorists might disagree but basically the I, iii and vi are tonic chords, the ii and IV are subdominant and the V (and vii dim) are dominant. We are all used to hearing and like chord progressions that make use of the relationships and movements between these types of chords.

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    there's many studies on this. here's one: hooktheory.com/blog/… – user34288 Apr 8 at 0:01
  • The asker never mentioned that 1456 is a rule, i.e. a good song must have 1456. He said that 1456 songs tend to be good, which would be disproved better with examples of 1456 songs that aren't good. – awe lotta Apr 8 at 20:44
  • I think this answer misses the point. Ther are songs written in other chords, but that does not answer the question itself. – mkorman Apr 8 at 21:39
  • @awe lotta foreyez edited his original post. He did originally say that these 4 chords are the rule and everything else is the exception thus my reply. – John Belzaguy Apr 8 at 21:59
  • @mkorman I believe my second paragraph does answer the question, I just didn’t go into detail about the many ways the relationships between these 3 types of chords work. – John Belzaguy Apr 8 at 21:59
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Chords, of course, are made of notes - and one way of looking at why notes have strong harmonic relationships between them is to look at the frequency ratios between them. Note pairs with simple frequency ratios have a strong harmonic relationship because some of the harmonics will coincide (assuming the timbre we're using has an ideal harmonic series).

The simplest ratios are 1:2, 1:4... and so on. These are octave relationships; we tend to hear these as 'the same note, but higher'.

The next simplest ratio is 2:3. That coincides with the musical interval of a fifth. If we imagine that our root note is 100Hz and our fifth 150Hz, we can see that the root will have harmonics at 100, 200, 300, 400, 500, 600, 700, 800, 900.... Hz, while the fifh will have harmonics at 150, 300, 450, 600, 750, 900... Hz. The harmonics in bold are in common to both notes.

And the next simplest after that is 3:4. That coincides with the musical interval of a fourth.

So any chord rooted on the fourth (IV) or fifth (IV) has a root that has a very strong relationship with the tonic.

We can also use these ratios to see why a major chord in itself sounds so strong. As well as the fifth (2:3) we have a major third (4:5) - also a very simple ratio.

So major chords based on I, IV and V are themselves based on simple ratios, and have roots that have relationships based on simple ratios. The upshot of this is that you will find that some of the harmonics present in chord V or IV are also present in the I chord. (Because chords are made of notes, and notes are made of harmonics, we can see chords as the superset of the constituent notes' harmonics.)

Looking at the IV chord itself - not only it is a major chord that contains the tonic note, but the third of the tonic chord acts as a leading note to its root. And looking at the V chord - its third acts as a leading note to the tonic. So motions between these chords are aided by the presence of these leading notes.

Taken as a set, the chords I, IV, and V contain all notes in the major scale. This is why it's often claimed that you could go better than Ed Sheeran claims in his quote, and use just those three chords to harmonise any major scale melody.

As to why the vi is popular - Richard has given some great reasons in his answer to Why is the vi chord so popular?. I would add that for whatever reason, minor chords are often associated with sadness, so adding the vi chord to your palette gives you an easy option for creating some emotional movement. As well as having two notes in common with the tonic chord, the vi also has two notes in common with the IV.

So, there are many reasons why those chords have strong relationships with the tonic, and can work well with each other.

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  • @RossMillikan thanks -'fixed', but I now realize I think I may need to pin down a bit more what I mean by simple ratios... – topo Reinstate Monica Apr 8 at 17:23
  • The point with the three chords is generally true until some accidentals appear in the melody. Such accidentals generally signal a deviation into a different scale, forcing the use of other chords than I, ii, iii, IV, V, and vi. For instance, when an F# note appears in C major, it's almost a guarantee that you'll need the double-dominant chord D major to harmonize it. – cmaster - reinstate monica Apr 8 at 19:25
  • @cmaster-reinstatemonica Sure - by "major scale melody" i (and i assume the linked question asker) mean we're only talking about melodies without accidentals. – topo Reinstate Monica Apr 8 at 19:35
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    How is 2/3 simpler than 3/4? What defines "simple"? Also the relation between the I and IV is that of a 5th, i.e. from IV to I to V are jumps of a 5th each. This is clear from inverting the 3/4 and bringing down an octave. – ggcg Apr 8 at 20:00
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    @ggcg 3/2 sounds good (quint) as does 4/3 (quart). Together they form the octave (2/1), so they are pretty much the same interval, harmonically. 5/4 sounds good (major third), 6/5 sounds good (minor third), together they form a quint (6/4 = 3/2) and are the basis for triads. 5/3 sounds surprisingly pure as well (major sixth). The small second (256/243) sounds bad. sqrt(2) sounds bad as well (the tritone) as it is nowhere near a simple fraction. In the end, it's a sliding scale with the most simple interval, the octave, at one end, and stuff like the tritone at the other. – cmaster - reinstate monica Apr 8 at 22:01
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Actually this goes back to ancient music and is expressed in the basic rules of Western music theory and harmony. You can get away with 3 chords for the most part, I, IV and V.

Consider that a melody will most likely be written using notes from the major scale of a key, in terms of degrees (1, 2, 3, 4, 5, 6, 7, 8). The 3 chords I, IV and V, cover the scale completely. The notes of each chord in terms of scale degrees are,

I = (1, 3, 5)

IV = (4, 6, 8)

V = (5, 7, 2)

Notice how the IV and V share a note with the I. This is no coincidence. The I chord can be thought of as the V of the IV and these groupings of notes from each major scale starting on the I, IV (an octave lower), and the V overlap making the three key signatures "compatible", they differ by one note in going from IV to I to V.

People have noticed for 100s of years, perhaps even 1000s, that "movement" in music is most interesting when we move around by jumps of a 4th or 5th. It is quite common for classical music to start with a simple main theme, or melody, played in the key of the piece with notes in the I chord then move the entire melody up to the IV and repeat. Moving to the V to return to I is a common device and is often considered the strongest form of resolution. In fact some old tunes just toggle from I to V, or V7 and back, never hitting the IV.

As for the vi, well that is in my opinion really just a substitute for the I since it is the relative minor of the key. Some may disagree but the I Maj6 chord and the vi -7 are identical and in Jazz they are subs for each other. In general a song can have either a major or minor character. In a minor key one can still harmonize the entire song with vi, ii, and III7, which are the i, iv, V7 of the minor key (using harmonic minor to get the leading tone). Including the vi in a song in a major key allows one to momentarily create a melancholy feel without a key change. The device is useful but not necessary.

There is an old joke that you only need to learn 3 chords to play Rock, in fact this is true of classical music and is in Tchaikovsky's text on classical harmony theory. So you see that one point of view is that people have been taught to use these chords for 100s of years and that makes them the most popular! Rather than it being a serendipitous mystery. Of course one can also ask, why did people gravitate to these chordal harmonies in the first place and that may be a harder question to answer. In part, it's a mark of the influence of Western culture. Helmholtz tried to offer a physics based explanation a lot of these trends in music based on looking at the harmonics contained in the vibrations of musical instruments. He was able to offer a "reason" for consonance and dissonance and some other features of Western music. In my opinion it falls short of a complete theory accounting for all Western trends.

The idea that you can cover the key of a song with just 3 chords that are each a 5th apart is fascinating but that does not explain your question about Pop tunes. In fact a lot of great popular music throughout the ages changes key and will definitely have more than three chords. However, the truly well structured tunes will still use the I, IV and V of each key and employ some clever device to execute the modulation from one key to another.

Going a step further one should note that all the other chords in a key can be reduced to a substitution of the I IV and V. It is not hard to see how, especially when you include 7ths, and consider poly-chord construction. For example the vi and the I are subs, but the iii is also a sub for the I. Putting them together (i, 3, 5) + (3, 5, 7) creates a I Maj7. You can find more about this is any book on functional harmony or Jazz chord subs. The point being that in theory there really isn't anything more to play with! I can take the entire circle progression in any key, a total of 7 distinct chords, and map it to a I IV V pattern. So, rather than the old joke that all you need is 3 chords to play perhaps the reality is that all you have and all you need is 3 chords.

That having been said one can rearrange many classic standards (and their plethora of ill gotten cycle hyper-extended progressions) in the Real book to have basic I IV V, or I vi V V progressions backing them up. In short, the chords don't really mean much and perhaps your question is a red herring. Perhaps there is NOTHING SPECIAL about these 3 chords, other than that they are sufficient to back up any tune, and the "Pop" ones have catchy melodies and hooks. One might even be able to write a pop tune with NO CHORDS! Just a capella voice. When someone says that they can back up any tune with 3 or 4 chords, depending on the source, they probably understand their music theory enough to know that you only need 3 to get the job done and anything else is gravy.

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I'll state what I notice about your theory. First off, those are the primary chords of the Major scale, except for that relative minor, and we have a preference for the sound of those chords. The predominant reason we use those chords for composing our music is because we like the sound of them when they are played together. That's the same reason our melodies use the same notes together, they have been time tested and they sound good together when we use them together. Some folks believe it's magic, and some believe it's inspiration from the cosmos, I don't know, maybe it is. However, I found in my experience that things become a hit because a lot of people like it, and it seems a lot of people like the sound of those chords together, which inspires songwriters to use them a lot. Simple as that.

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I'll take a stab at this question, which is quite complicated to answer. The simple (but unsatisfying) answer is that songs with these chords are popular because that's what we're used to hearing in popular music today. There's no necessary acoustical or theoretical reason why these chords must be "superior" to all others. Many other musical systems existed historically and continue to exist today, which produced music that was immensely popular in various cultures without centering on these chords (or not centering on chords at all).

The slightly more nuanced answer is that once you accept the major diatonic scale with triads built on each degree as a theoretical system (again, something that's a product of complex historical and cultural forces), these four chords -- out of seven possible -- give you the most variety of progressions that incorporate both traditional chord motions and allow novel permutations.

That's the TL;DR version. Below are further details.


The Danger of Circular Reasoning

It's easy to fall into the temptation to try to justify one's current culture and preferences by appeals to some sort of external logic. Ultimately, however, this can lead to a lot of circular reasoning. For example, some answers postulate that I, IV, and V are the best "central" chords because they cover all notes of the major scale within them. While that seems a reasonable criterion for harmonization possibilities, it doesn't explain why, say, I, ii, and V couldn't be used as an alternative system, as they have the same characteristic. (And there are other examples of chords that cover the scale.) Similarly, one could note things like ratios in the harmonic series and postulate some connection between the fifths and fourths that show up there and the connections between fifth/fourth root motion in triads. But again, there's no clear connection -- psychoacoustical research does show that the structure of the harmonic series can lead to consonance and dissonance of harmonic intervals, which is one reason for the existence of triads in modern pop music. But why should that have any connection to consecutive intervals between chords that aren't sounded together? And why would only the intervals between the roots be important?

I'm not saying there can't be some truth in some of these explanations, but a lot of them are taking a system we already have in place and creating an ad hoc justification after the fact.

I/IV/V Was Not Universal (nor was the ubiquity of diatonicism or major mode)

The first thing we must accept is that Western pop music is only one possible musical system that developed through a lot of historical and cultural processes over centuries. After that, we can begin to take apart the reasons why it developed the way it did, and why things like the I/IV/V set of chords became so common.

There are lots of other assumptions we need to work under here, like the preexistence of something resembling the seven-note diatonic scale (developed in ancient Greece and gradually transmitted over the millennia in various forms), the usefulness of triads (a concept only developed in the early 17th century), etc.

But let's pick up the story around the year 1700, when popular music ("folk music") of Europe sounded a lot different from what it does today. Composers of the 1600s would be just as likely to pick I/ii/V as a central group of three triads in a major mode, rather than I/IV/V. The reasons for this are complicated (and would take us down even more digressions), but it's important to realize that I/IV/V was a relatively late development in Western music.

As triadic theories developed in the 1600s, I and V were obviously going to be central, as they had framed the structure of cadences since they began to resemble modern form in the mid-1400s. But the next-most-important chord was not very clear. The role of ii and ii7 in cadences before 1700 was more prominent than IV, and the more modal character of folk music of that time made more heavy use of minor options.

That's another assumption in the question -- why is major mode dominant? Why do we analyze the chords as I/IV/V/vi and not i/III/VI/VII? Indeed, many modern pop songs emphasize the one minor chord as more of a tonic/home, so that ambiguity is present in pop music. But the emphasis on the major mode as a theoretical center didn't begin until the 1700s. Today, we tend to think of the minor mode as "inferior" somehow or at least denoting some negative emotions (sadness, distress, etc.), whereas historically before the early-mid 1700s this was not true. And the minor mode developed lots of other non-diatonic chord options, which resulted in a richer harmonic palette. Yet the theoretical simplicity of the major mode (along with the newly formulated arguments on the basis of supposed connections with the harmonic series) placed major at the center of a lot of music theory by the mid-1700s.

Another assumption brought up in the previous paragraph is that of diatonicism. Today, oodles of popular theory books start with an assumption that chords are built on diatonic scales, and harmony is therefore essentially diatonic. Many college courses start with a semester or even a full year focused on diatonic harmony. But this is an anachronism when used to discuss classical music, which was definitely not diatonic, even in its simplest conception. Even little 5-year-old Mozart knew to put a #4 leading to 5 on his half cadence in the middle of his minuets. So-called "chromatic harmony" was not a more advanced element tacked onto a diatonic system in baroque and classical music. Instead, chromaticism was fundamentally "baked in" to even the simplest exercises taught to beginning students. Our "diatonic" harmonic system is a sort of myth, created by later pedagogues -- prior to 1800 or so, monophonic chant was founded on diatonic scales, but polyphonic harmony was decidedly not.

The Historical Emergence of I/IV/V as Central Triads

So when did all of this change? A lot of it came in with the theories of Rameau in the mid-1700s. He emphasized the primacy of analyzing music as built on triads. In his initial theories, he didn't foreground IV, but his later theory finally builds the I/IV/V structure as central to creating harmony in a major key. (This comes out of a sort of mystical obsession with ratios, which frequently ignored or reinterpreted actual musical practice to fit his theories.) He uses the harmonic series to create an ad hoc justification for the major scale and triads. Later in the 19th century, Germanic Stufentheorie (scale-step theory) builds this concept of diatonic triads on each step of the scale, which allows the creation of a diatonic world, as discussed in elementary theory textbooks today.

One could write an entire book on why I/IV/V gradually came to be central chords, but this outlines a bit of it. And then this new system began to spread in popular music. In various countries, it happened on different timelines and in different ways. In the U.S. (most relevant to global pop), my guess is that it was mostly promulgated in the 19th century through the harmonic vocabulary of sheet music pop songs (think Stephen Foster) and revivalist hymnals (where the hymns were composed to make congregational singing very easy, and the composers were not necessarily versed in complex harmonies). These trends supplanted the earlier modal styles (often infused with more minor mode) and systems with a more varied harmonic vocabulary. One can compare ballads written in the mid-1800s with those in the mid-1600s to see how radically the I/IV/V major-mode theoretical chord system changed popular music. Pockets of older systems survived in isolated communities, for example, the shape-note singing of the American South which preserved hymnody with more varied harmony and texture (and which still contains some practices closer to 17th-century hymnody).

I've skipped over a lot here, but one other important element to bring up is also the role of Spanish guitar in cementing a chordal view of music beginning around the 17th century. (This followed a rapid dissemination of guitars around Europe, as an alternative plucked string instrument that was louder, fun to play, and perceived to be easier than the lute.) Early alfabeto notation used predecessors of modern chord symbols, which may have influenced the increasing trends toward chord classification and eventually Roman numeral development in the early 19th century.

With the minor mode, chromaticism, and a variety of harmonies increasingly abandoned in favor the major-mode diatonic system that borrowed the theories of Rameau (and others who build on such theories) to emphasize I/IV/V, the stage was set to gradually take over a lot of popular forms in the 19th-century as sheet music and hymnals spread these structures to the masses.

(Note: I should qualify all of this by saying that this wasn't just caused by Rameau and his followers promoting this new theory. I've necessarily oversimplified things. Rameau was a product of his era, and there was already popular music using more major mode and using I/IV/V developing alongside these theoretical systems. But those are harder to trace than treatises that systematize such developments.)

What about vi?

So far, I've neglected vi. It was a chord that had been used for many centuries in "deceptive cadence" motion, so it's an obvious choice for some variety. But why settle specifically on I/IV/V/vi as the vocabulary for modern pop?

The proceeding discussion was necessary to establish that the concept of a major diatonic scale with chords built on each scale degree is NOT the only possible musical system or the most "natural" one -- it was a very gradual historical development. But once we have that major diatonic scale with triadic harmony, why choose these particular chords?

Let's look at the alternatives. The vii° chord has functioned since the 17th century primarily as an incomplete V chord. Since we need V to make the same sort of cadences we've been making in Western music for 500+ years, vii° gets us nothing significant more. That's aside from the fact that it is diminished and therefore branded in modern music theory as somehow deficient compared to the major and minor triads.

Then we could look at iii. But the role of iii started to be downplayed in the major mode since before the concept of the triad even emerged. Studies have shown that it decreases in usage in the major mode even in the early 1500s. It was just never a significant part of the standard harmonic vocabulary that developed for the major mode. (Mozart could -- and did -- write an entire symphony in major without even using a iii chord.) Aside from certain uses in long sequences, it was just never that common.

So the only other chord left is ii. As noted above, ii was actually a more common option than IV in earlier styles as a predominant, but Rameau undermined that in favor of IV. (Subsequent theorists have found various other ways to justify ignoring ii in favor of IV, frequently invoking abstract principles that had nothing to do with historical musical practice. Nevertheless, IV gradually caught on.) Restoring ii does give us a ii-V-I turnaround, which is very popular in classical, jazz, etc. styles. And it is an interesting "more minor" predominant that could color the harmony. But there's not a lot going for ii when you already have IV. One could imagine an alternative universe without Rameau where we used the four-chord group I/ii/V/vi instead, which makes for a nice circle-of-fifths vi-ii-V-I sequence. It would be a more minor world, and one that sounds more "modal" than the way that music developed over the 18th and 19th centuries.

Anyhow, if we accept the I/IV/V axis for the major mode to revolve around, vi is the most logical next chord. Aside from deceptive cadences, it gives a hint at relative minor as well as a "minor turn" in general to contrast with the other major harmonies.

In pop music in particular, I also think its inclusion partly comes from the prominence of the descending thirds sequence (I-vi-IV) over the circle-of-fifths sequence (vi-ii-V-I). Everything from doo-wop and bubblegum pop to various ballads in the 1950s began to center around the traditional thirds sequence cycle. I'm not sure why this became so popular, though the fact that there are more common notes held in the descending third sequence was always a reason for its popularity (and gives it flexibility for melodic harmonizations). You can't play a lot of those songs without vi, though you can often find substitutions for ii when it occurs (either IV or vi).

The Staying Power of I/IV/V/vi

Hence, we arrive at a four-chord I/IV/V/vi minimal vocabulary. I think it has had staying power in pop music because of its variety. You have a minor chord for contrast, as well as the deceptive cadence (V-vi) and descending thirds pattern (I-vi-IV). You have a nice strong predominant (IV). You have the modal ambiguity I mentioned earlier, where vi-V-I can easily be reinterpreted as the move to relative major (i-VII-III) that shows up as a standard musical pattern since the 17th century. You have a nice mixture of possible root motions: fifths/fourths (V-I and I-IV), thirds (I-vi-IV), and seconds (IV-V-vi), which adds to the feeling of harmonic flexibility with a minimal chord set. And, as we've seen with the development of patterns like the Axis of Awesome progression (I-V-vi-IV) or the "sensitive female chord progression" (vi-IV-I-V), the various permutations can yield more than just standard authentic cadence (IV-V-I) and 50s pop (I-vi-IV-V) progressions.

You can't get this amount of variety by using another subset involving ii. You'd either end up with a more symmetrical but more boring I/ii/V/vi or a pattern less suited to pop progressions and duplicating the predominant function (I/ii/IV/V). As mentioned, the other diatonic triads (iii and vi°) were just never real contenders given their lesser importance historically.

So, through process of elimination, once you've settled on the idea that music should use the simplified major diatonic system with triads (the assumption in pop theory for the past century or so), the I/IV/V/vi system just gives greatest "bang for your buck" in terms of variety and flexibility, if you're not willing to learn or use more chords.

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  • what an answer! – user34288 Apr 14 at 3:21
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Tonic, dominant and pre-dominant. vi is much less basic I think.

Yes, that's the bare bones of functional harmony I suppose.

I can't see any theory in your links. Just a rather clumsy way of (partially) notating the songs.

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Sorry to answer my own question but I was just reading this article which made a lot of sense to me. In it they say the the IV and V are both a fifth away from the tonic. This reminds me of a question I asked some time ago. And the fifth is just the most pleasant sounding interval.

And the vi is popular because as the relative minor of I, it also has the IV and V chords in its key (which from the perspective of the minor is the VI and VII), the other minor chords don't have those two.

So altogether those 4 chords make a very stable relationship.

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  • The fact that the IV and V are both a fifth away from the tonic can be seen in terms of frequency ratios too. A fifth is 2:3 - if we double the bottom note's relative frequency (move it an octave up), we get 4:3 (i.e. a fourth). – topo Reinstate Monica Apr 8 at 6:59

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