I play a song in either C major key or A minor key.

Usually I determine the root (C or A) taking into account clues like:

  • The happy or sad feel of it all
  • The first chord (C or Am)
  • Stereotypical tensions like G7-C or E7-Am

But I came up with a pretty jazzy baroque thing starting in C6 or Am7/C, does not feel exactly sad or happy, and does not have usual tensions.

How can I rationally infer the root? What would follow a pro? How to tell whether the first chord is a I6 or a vi7 (Im7 or i7 in key of A). Despite of several notations Nashville, Roman, etc.

  • 2
    "Root" refers to the basis of a chord. The term for the basis of a scale or key is "tonic"
    – Tom Serb
    Apr 29, 2019 at 13:34

4 Answers 4


You don't need to start on i or I on any piece of music and one chord alone will never tell you what key you are in. You need more context to actually know what's going on.

The rest of the progression will tell you what key you're in especially when you come across dominants chords and cadences. If you encounter a lot of E7 chords I'd expect it to be in A minor. If you encounter a lot of G7 chords I'd expect it to be in C major. It is also possible for the piece itself to weave in and out of those two keys especially since they are very related.

C6 is a very common substitution for Cmaj7 so if I had to guess, I'd bet you were in C major over A minor.

  • 1
    Never come across C6 substituted for Cmaj 7. But it is another reincarnation of Am7. Ambiguity!! As I've no doubt quoted before - look at Fly Me To the Moon. C or Am? Who knows? Who cares?!!
    – Tim
    Jul 19, 2015 at 18:15

Check your phrase ends/points of cadence, also your "roof" and "floor" (the successions of highest notes in the treble, lowest notes in the bass). Dom is quite correct that a lot of music doesn't start with the tonic. Starting deceptively has been a valid technique since at least C.P.E. Bach and Joseph Haydn.

Establishing a tonality is often an active process. Frequently when you are doing so, you are also establishing the opposing tonalities that will serve as large-scale dissonances (or tensions, if you want) in the piece. In the earliest sections of a piece, this is usually by suggestion: relative to the weight placed on the tonic, cadential progressions of secondary keys will tend to be "incomplete" in some way, either by occurring in rhythmically weak spots (midway through a phrase, for instance), or by using weak cadences (half-cadences, deceptive cadences, cadences with chord inversions) or both.

A lot of music in the major isn't conventionally happy; likewise a lot in the minor isn't conventionally sad. Most music, major and minor, exists in a continuum of Affekt between the two poles.


Patrx2 and Dom's answers are both very good. To add to them:

Usually I determine the root (C or A) taking into account clues like:

The happy or sad feel of it all

I think Patrx said it quite well, I would add that minor sounds darker to most people than major, but adding meaning and emotional content to the sound is the function of the artist, it is not dictated by the chords. Darker often gets associated with sadder, but to quote Van Gough "I often think the colors of the night are more vibrant and alive than those of the day."

The first chord (C or Am)

Is as mentioned is not a reliable indicator. However, in popular music the root of last chord will almost always be the root of the song. The chord quality may have been substituted (e.g. its not uncommon to write songs in minor keys and then substitute all the chords with major chords on built on the same root.)

Stereotypical tensions like G7-C or E7-Am

The tension and release provided by V7 to I (and the accepted substitutions for it e.g. tritone, common tone, etc.) is more than just a stereotype, its part of the structure of western music. Its just an inescapable part of how we are culturally conditioned to hear music. Regardless of how modal, atonal, avant-garde, or experimental a piece may be, it still exists in a world where it is specifically playing against the listeners expectation of a satisfying old school authentic cadence.

V7 to I is less of an indication that a key has been established, its simply how a key is established, when it is placed on strong beats in important parts of the songs overall form.

To use your example:

As I've no doubt quoted before - look at Fly Me To the Moon. C or Am? Who knows? Who cares?!!

I wish I had the recording, but assuming the chords on ultimate guitar are correct http://tabs.ultimate-guitar.com/f/frank_sinatra/fly_me_to_the_moon_ver5_crd.htm I would say the song is clearly in A minor. It ends on A-7 (starts on it as well), and is constantly going E7 to A-7. Of course those chords could be 100% wrong, I'm basing my call here on that specific link.

I feel your pain though, I distinctly remember that what the hell is going on here? feeling trying to figure out *God Only Knows" off the Pet Sounds CD.


In Phil Smith's answer he points out that the last chord in Fly Me To the Moon is actually a C not an A-7 as it is transcribed on the link I referenced earlier. In which case I will stick to my theory and say if the last chord is a C, the song is in fact in C not in A minor. If the chords on the linked page were correct, the song would be in A minor, but apparently they are not correct.

  • Jay Sklyler, you very astutely wrote: >in popular music the root of last chord will almost always be the root of the song. but then you go on to say Fly Me To The Moon is in A minor when the last chord (excluding the turnaround) is C. Fly Me To The Moon is definitely in C. Or whatever key you're in. The song people always get wrong is Unforgettable. Assuming it's in the key of C, most people assume it's in G (all those F#s, you know). But if you analyze it in the key of G, it's totally complex. In the key of C, it's straightforward. The F to Fmin is just the standard IV-IVm of American Popular
    – Phil Smith
    Jul 19, 2015 at 23:43
  • Phil, I don't have the recording. like I said, I just analyzed the chords on the transcription I included a link to above. That transcription has the last chord of the song as an A-7.
    – Jay Skyler
    Jul 20, 2015 at 1:33
  • I've always questioned 'Unforgettable'. Where does it stop feeling in C and feel like it's now in G?
    – Tim
    Jul 20, 2015 at 5:55
  • Yeah. I didn't mention final cadences because I got the impression that OP was trying to figure out where to take an initial idea for a piece or song, but I agree with your observations, especially with regards to dominant relationships. A work's tonality (for a work of more than trivial complexity) is created by a hierarchy of tonal relationships and tonal assertions of varying strength, and it takes all of the elements of music working together to create that hierarchy of strengths, soit progressions, soit beat placement, soit dynamics, soit registers.
    – user16935
    Jul 20, 2015 at 6:43
  • The last C could well be a piccardy third :)
    – Whimusical
    Jul 20, 2015 at 15:05

A good way is to try and write a simple bassline, and see what sounds good. It's easy to come up with note clusters higher up where the root note is ambiguous, but much harder (but not impossible) to hide from it lower down the pitch scale.

Also, make up a melody that fits your chords. Then write a bassline that fits that same melody, and that could point you in a good direction.

Alternatively, this way is much more subjective, but it is honestly the way I would do it. And that is just to try and work out what chord "feels" like home. You've already talked about what chord a piece begins on, but if you wiggle around your chords to end on an Am, or the same for a C, which one feels properly resolved?

If you mentioned cadences. So does E7->Am feel more like a resolution or a modulation (same with G7->C.)

IF that all fails, play with the parallel minor or major of your potential keys. If you're in C and you modulate to C minor, it's a mood change, but not odd-sounding if you lead into it properly. The same with Am to A major. It's cheesy and you probably won't want to use it in your context (of jazzy baroqueness), but it will tell you where you're at.

Because (usually but not always, as is the disclaimer for most musical "rules")

C major -> C minor sounds a bit mysterious and odd Am -> A major sounds a bit cheesy C major -> Sounds like a modulation Am - > Cm Sounds like seriously WTF just happened.

Also, minor=sad is often wrong. ESPECIALLY with flat 7ths.



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