Sometimes, when I'm watching any TV show which has a live hired band for accompanying and they have a musician guest, the host will ask for them to sing something on spot (that wasn't really planned), and they'll say to the band "please give me C Major [or whatever key]".

Then they'll start singing and the band will typically join him/her after a few notes. How do these guys figure out the entire chord progression for the song instantly?

(I'm obviously interested in situations like this that aren't staged.)

  • 25
    In addition to legitimate answers to how musicians develop and access this skill, TV producers aren't against staging the show to seem like this is the first time the musicians are seeing it. Some shows will pretend, some will be legitimate. Top studio-quality musicians need to have this versatility though.
    – SRiss
    Commented May 16, 2011 at 6:07
  • 2
    I'm sure that sometimes it is really staged. I failed to state the premise that, for the sake of the question, I'm obviously interested in the situations that aren't staged =D Commented May 16, 2011 at 13:22
  • I suspect the main trick is to be lazy, and follow the lead. After one repetition of the chord pattern, often just 4 bars, you got it and can join in properly. Commented May 16, 2011 at 14:38
  • 1
    Should this be made a community wiki? Commented Aug 28, 2011 at 12:40

14 Answers 14


There are formulas and sets of harmony formulas that musicians know of. ie. Chord Formation. I, IV, V7 sets of harmony; Chord Substitution; Fifth Motion, Dominant motion; Diatonic Cycles of Fifths, Chord Tone Substitutions, etc.

Each chords in each set have their own characteristics that you need to know what they represent. I can be indicative of what each chord's character are like but the fastest way to teach you that is through you experiencing it.

With that, once someone says: Gimme a C or whatever, immediately the musician knows the set of harmony ideas they must employ. And with their sense of feelings and hearing they will know what the next chord should be.

Of course they do make mistakes. That is where they correct themselves along the way in real time. In my place, we call it 'bluffology" - bluff our way through. Done properly, most people will not know our mistakes.

It does takes time to acquire such skill but the mindset must be tuned that way first.


There are three possibilities:

  1. The musicians are "faking it" based on their knowledge of theory. This notion may be romantic but in my experience it is rather unlikely. There's simply too much that could go wrong. This isn't a jam session or a concert, it's a TV performance to showcase a singer. That said, in other situations they might be perfectly willing and able to "fake it" (that's where the term "fake book" comes from, after all), in which case Play By Ear's answer applies.

  2. The musicians have played the song before (probably in a different key and are transposing it in real time). Rather likely. Professional musicians have a repertoire in the hundreds or thousands of songs and are fully capable of transposing.

  3. They knew about the song before the show started, i.e it was staged. Very few things on TV are totally "on the spot" and unrehearsed. I find this to be the most likely explanation for this particular case.

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    For an example of what happens when performers are really put on the spot, VH1 had a series "Cover Wars", the first round of which was "The Human Jukebox", where the band had to play (or fake) each song given by the judges, on the spot.
    – KeithS
    Commented Mar 2, 2012 at 15:51

The short answer is - because they can hear how the song goes, and they know how to translate those pitches into a chord progression on their instrument that quickly. Because they went to music school or because they have many years of experience or both.

It's not faked or rigged or a trick.

While it does look like magic, it is a surprisingly common skill for professional musicians at the level you suggest - appearing on a national television broadcast for example. One would imagine that a certain level of recognition of proficiency is required to be invited there in the first place. In fact, it is expected that they would be able to do that. Just like you expect your dentist to recognize gum disease when he looks in your mouth.

Would one ask "How did my plumber know were to find the clogged drain I had, he had never been to my house before?" or "How did my doctor know that I was deficient in Vitamin D?". Because they have years of training and experience and know what to look for and how the system that they work with functions.

Believe it or not, being able to aurally recognize a chord progression is a learn-able, teachable skill. It takes practice, just like medicine or computer programming or chemistry, but there is a stepwise reproducible method to learn how to do it. So couple the knowledge of how music works with years of experience and you get someone who can hear a song for the first time and play along with it.

This skill is one of the many you are taught when you go to a music school and spend 4 years there. You take classes like "Ear Training" for semesters and semesters. And they even test you. They play songs at a piano and you sit in the class and have to write down how they go, just by listening to them.



Here is an example test:


The instructor would play those phrases, and you would sit in class and have to write what he played. Then you turn it in and get graded. As you progress through your four years of music school, the examples get more and more complex until you have to listen to things like entire string quartets or symphonic pieces and notate them. All the parts. Of every instrument.

Despite music being an art, there is a great deal of the mechanics about it that humans have been thinking about and documenting for more than one thousand years, so most of "how do I do X" has long since been written down and is very well figured out and documented. It isn't magic, just 1000 years of ten million-million collective man hours of human beings thinking about this subject, writing things down and passing it on.

While from the outside it does sometime look like voodoo when someone does it, if you sat with a teacher who said "First you do this, then you do this, then you do this" every day for four years (or much much longer), it would not look so magical.

  • Your answer makes a lot of sense. However, a piece of music is not as spontaneous an event as a clogged pipe or mouth condition. Somebody created it. I just think your answer was too "ultimate" regarding the previsibility of music in general. Of course, the very question I asked implies that this previsibility exists in some degree, though. Commented Oct 3, 2011 at 0:14
  • @RafaelAlmeida Music certainly can be that spontaneous. The simple answer to your question is, the musicians know what sound they want to make, and they know how to make that sound.
    – slim
    Commented Mar 2, 2012 at 11:04
  • You are very trusting!
    – Laurence
    Commented Dec 9, 2016 at 13:00

Assuming they don't already know the specific song (it's quite likely they do), it's possible it's a contrafact: a song based on the chord progression of a jazz standard; e.g. 12-bar blues or rhythm changes. Or a pop song using a common progression with just 3 or 4 chords; e.g. I I IV V or I V IV V or I IV vi V or I iii IV V, etc

  • I've seen this mostly with pop songs. I imagined that they probably base their progression choice on a "standard" song. But this leaves the question, how do they decide which? Not less importantly, how do everyone agree in the choice, seemingly wordless? Commented May 16, 2011 at 13:51
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    @Rafael: I can't resist spreading this as a demonstration that you can go a long way with 4 chords (even 3).
    – ogerard
    Commented May 18, 2011 at 7:07
  • @ogerard - Your link says it all :) Commented Jul 26, 2011 at 9:22
  • You forgot I V vi IV
    – mathlander
    Commented Oct 11, 2023 at 23:36

TV-show bands research the music of guest artists beforehand, including the keys in which they work. They do this for a few reasons, not the least of which is the off chance that there is an improvized request for a tune. But on the whole everything is staged including what looks to be a spontaneous jam. The best perfomer in the world will sound bad with bad accompanyment or being forced to sing or play (especially sing) in an unfamiliar or just plain wrong key. They earn their keep by their reputation and media exposure, and nobody takes a chance on messing with their rep.

  • Let alone without warming up for live TV.
    – yossarian
    Commented Jul 27, 2011 at 21:21
  • No they don't. Certainly not to the degree of polish we see in these 'spontaneous' performances. It's showbiz!
    – Laurence
    Commented Dec 9, 2016 at 13:01

You can make a pleasing accompaniment to most melodies using three chords: I, IV, and V.

The reason this works is that between them, those chords have all of the notes in a standard scale.

For example, if the song is in the key of C major, then the I chord has the notes C, E, G, the IV chord has the notes F, A, C, and the V chord has the notes G, B, D. All seven distinct notes of the major scale are represented: C D E F G A B

So if the person singing or playing the melody plays a B, then you can play the V chord, and it will sound ok because B is in the chord. If they sing or play a G, you can choose between I and V because both chords contain the note G.

As you listen, you can get a feel for where the song is heading, and when the note G comes up, that prediction about where the song is going next helps you decide whether I or V seems like a better fit. For example, if it seems like the piece is nearing the end, you probably are going to encounter a V-I cadence or a IV-I cadence.

As you get more skilled, you can change it up a little bit, use different chords, make it more complex, but in a pinch, you can harmonize almost anything with I IV and V. There are exceptions, but for pop songs exceptions are rare.

Part of the neat thing about harmony is that there are many different ways to harmonize a melody that can be pleasing. So there are many possible ways to accompany a melody that will work. If there is more than one person accompanying the melody, they will have to coordinate a little bit. If they are in a band and have done this before, they will probably have a sense of which chord progressions the other band members like to use. It is possible for there to be mixups though, where some band members play one chord, and other band members play another. It is also possible to guess wrong about where a melody is heading and play a dissonant chord. However, dissonance is part of music, and if this happens, you can continue on to a more consonant chord with some filler notes and pretend you meant to do it all along.

So in summary, the accompanists probably don't know the chord progression for the whole song all at once. They probably can project a little bit into the future. They probably have a standard set of chords that they use in these situations, (For example, I, IV, and V, or another set of chords that covers all of the notes of the scale,) and they fit the chords to whatever notes the person sings or plays. The resulting harmony may not match the way that the person singing or playing the melody would usually harmonize the song, but it will sound pleasing nonetheless.


I'm an accompanying musician and I do this all the time with the musical styles that I'm familiar with. Have you ever faked singing along with a song that you've never heard before? It's the same thing with musicians writ large.

The very brief gap in the first bar is where the musicians establish the key, the style and the general form of the song. All songs are composed of cliches, predictable chord progressions, rhythms and melody fragments that make up the style of the song. That's why reggae doesn't sound like Xmas carols.

Once the key and style are established, the musicians will very cautiously start adding suitable harmony, hanging back from the very front of the beat so that they have a few hundredths of a second to determine if they need to change their guess. In various musical styles there are also certain figures that are common for going to a particular chord. Once the song has been played through once, the form, style and harmonic progression have been established and the accompanying musicians can play with confidence.

As an audience member, this whole process can be difficult to pick up, unless a song takes an unexpected turn. As performing musicians my wife and I take great enjoyment in watching live performers fake their way out of the occasional "clam" to avoid a "train wreck."


Reflecting upon the above answers, if a song is in a major key, using only the 3 major chords available i.e. I IV V when the part of the song you are playing feels like it is about to change chord (experience tells) there's a 50:50 chance of hitting the right chord next. Pretty good odds!! By using the other 3 chords as well -IIm IIIm VIm a fairly comprehensive choice of chords is available. If the player feels the tune needs to go from maj. to min., there's still a 33% chance of hitting it right. Experience is all....However, when you try to busk something which modulates wildly, expect trouble unless you know the map of 'new keys'.


I should make reference to the Nashville Number System, a system of pop music notation developed for country music performers, both background singers and instrumentalists, for use in places like the Grand Ole Opry stage show and widely used in the Nashville, Tennessee music industry by recording studio session musicians in accompanying singers. The premise is that once the chord progression for a song has been notated in the Nashville Numbers System, the performers can instantly transpose the song and perform it live in any key asked for by the singer. This presupposes some skill on the part of the performers, although country music is known for not being very complex.

The link above is to a commercial textbook devoted to explaining the Nashville Number System.


It is actually possible to practice sight-reading. What you do is you get as much new music as possible and try sight-reading it. It's good to start with music that is easy; I began with the Reader's Digest songbooks. And/or music you really like and are motivated to learn; for me that was Bach's Preludes and Fugues... But don't spend too long on each piece, move on to the next one. After a while you find that you're getting better and better. I did this when I was about 14-15 years old on piano, because I realised my music reading wasn't very good. After a while I found I could sight-read better. Eventually I became a piano accompanist - for many years this was my main musical job - and these days I can sight read very well. The answers above are correct, in that one tends to recognise patterns and automatically play them, also tend to use 'bluffology' when it goes wrong, as it sometimes does. But I thought I could add something to those articles, by saying how you can actually get to the point of being able to sight-read.


I do this. Basically it comes down to developing your ears. I can offer twelve useful tips:

  1. Learn to recognise all intervals instantly.
  2. Learn all your scales and arpeggios without needing to look at sheet music.
  3. Practice often with no written music. Challenge yourself to improvise in a certain style and key (or sequence of keys) convincingly for a few minutes at a time.
  4. Learn songs. Then learn more songs. After that, learn a few more songs. Actually memorise them, and now and again go back and revisit the ones you forgot.
  5. Don't worry about "perfect pitch", it doesn't really matter, but have GREAT relative pitch. So when you hear fragments of melody on the radio, in a shop, whatever - get the habit of mentally "playing them" on your instrument. (This is a follow on from 1.)
  6. Listen actively to music - meaning, really observe what is happening, what different musicians are doing to support the overall performance, how the song is structured, when sections repeat and so on. Avoid "passive" listening as that creates a bad habit.
  7. Study different styles and what great players on your instrument do in those styles. I play sax and clarinet - I used to play in a band doing funk, soul, reggae and so on, and a lot happened spontaneously. I developed a vocabulary of licks in those styles based on listening to classic records. (Sax players do certain very common things in a reggae band which are different from funk or blues.) Steal mercilessly from every possible source!
  8. It helps to play some piano, guitar or bass - then you can look at their fingers which gives you more clues! Anyway you need to play a harmony instrument to learn harmony, And you must know harmony, and common chord sequences.
  9. Put yourself in situations where you can develop this skill. You will screw up sometimes. Don't worry, just keep doing it. Learn to make your mistakes sound like you meant them!
  10. Keep practicing.
  11. Keep listening.
  12. Have fun.

  13. Bonus tip : put on a recording and see how quickly you can pick up what is going on and play something that fits with the other players on the tune.


Hmmmm ...

  • A TV show

  • Musician guest (obviously everyone would know who the musician guest is) Spontaneous singing

    .. you can bet the band would be primed, for several popular tunes, otherwise they all look terrible on TV. Forgive my cynicism.

However if a musician does know a song (ie has heard it, perhaps can hum the tune) then there'sa a good chance of being able to "find" it spontaneously on an instrument, using experience.

It's a bit like singing : If you've heard a tuneyou can probably sing it spotaneously. It's one more level of experience to be able to play the basic chords etc on the instrument, especially if it's a simple song.

  • My speculation would also be that the singer would do well to pick a song which can fit a common chord progression, because they don't want to look stupid when the band go wrong because they chose to sing something which modulates in an unusual manner. But on live TV... they probably did improvise it in rehearsals, and now they're going to just do the same thing again. Commented May 21, 2014 at 10:10

In my case it was a skill I developed by participating in countless jam sessions both with friends and strangers. I can follow others as they improvise and they can follow me as I take the lead. Chord leading comes into play quite often, as does having an extensive repertoire, and knowing how to transpose from one key to the next on the fly. Also having a strong sense of relative pitch and knowing chord structure and the resulting sound of it's harmonies helps a lot. Often one or two members of the orchestra can take the lead and others almost instinctively know how to go along. This can happen with varying degrees of success with almost any group of players, but it's only the proficient players that collect a check from the broadcasting companies.


Simple: a lot of education and a lot of experience. Over time, we are exposed to every sort of music variation and oddity. Eventually we get to the point where a piece, even though unknown, can be rather predictable. Notice when people are jamming they seem to manage some pretty tight endings simply because they've played a lot of endings.

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