I am working my way through music theory. I play acoustic guitar - or try to.

One of the exercises was in C and mentioned a Fmaj9#11 chord. So I dutifully worked out the notes for the chord and was pretty proud of myself figuring out F A C E G...but I wasn't sure of the last note.

Because it's in the key of C I would have expected the 11th note to be B#. Since B is the 11th note (counting up from F in the key of C).

But it's not - it's B (according to what I can find on the net).

Then I realise that a Fmaj9#11 chord is going to be different depending on the key.

If it was in the key of F then the 11th note is B flat. So that would make sense.

But in the key of C the 11th note is B natural. To sharp it would be B#.

So if someone says - play a Fmaj9#11 then one would need to ask what key one is in?

And then why doesn't my Fmaj9#11 in the key of C not have a B# in it?

Thank you

Update: Thanks for your help everyone.

I had to take this away and think about it for a while. But finally it made sense.

You see I learned what I know from a video, working in the key of C. He showed us how to add 3rds and 5ths to each note of the scale. Based on the key of C.

e.g. CEG DFA EGB etc

And the result was that D, E, A, B had minor thirds - so they were minor chords. That was the end of the video.

I figured that we work out chords based on they key of the scale. Which kind of works. Until it doesn't.

But instead we work out the chords from the major scale of the chord, regardless of key. So for minor chords we would flatten the thirds. Kind of the same result but easier to understand. Especially when the chords get a bit more complex.

Plenty of time to work on it with this damned virus too.

But do please correct me if I am wrong.


  • 4
    "Then I realise that a Fmaj9#11 chord is going to be different depending on the key" I don't know how you 'realised' that, but it's not true. Chord symbols don't change based on the prevailing key - they provide empirical formulae for a chord built on a given root.
    – user45266
    Commented Mar 12, 2020 at 0:52
  • This sort of duplicate several existing questions about chord symbols, like music.stackexchange.com/questions/94307/… Commented Mar 12, 2020 at 21:06

4 Answers 4


Chord names relate to the root note of the chord, not the key. This makes sense and is helpful: it means a chord name always tells you exactly what intervals are in a chord; it means you can have chromatic chords within a key.

So, for instance, a #11 is always an augmented 4th above a root (or some octave displacement of this), no matter what the key or what degree of the scale the chord root is on (if any). Another example: a #11 on any kind of Eb chord will be A whether we are in Eb major, Ab major, C major, D major, B minor, F# minor, any other key, or in a piece of music which has no clearly defined key!

  • 1
    In other words, when reading chord names, use the scale of the chord root, not the song :) Commented Mar 12, 2020 at 2:11

It's a sharp eleventh above the chord root.

So with Fmaj9#11 you have a "sharp" eleventh. Notice the quotes. The sharp can be misleading, because it give the impression an actual sharp would be used to spell the chord. The default would be an 11 figure assumed to be a perfect eleventh. The # means raise it a half step.

But, what if the root were Bb and a chord like Bbmaj9#11? A default 11 would be an Eb so #11 means raise Eb by a half step which gives us... E natural! So, the chord symbol uses a # but the actual spelling uses a natural. That is a misleading aspect of chord symbol conventions.

Suffice to say it would be better to call it an augmented eleventh.

If the root were F3 the #11 (an augmented eleventh) would be B4 (a B natural.) For all practical purposes it could be a B natural in any octave above the F root.

BTW, this kind of jazz chord symbol is not relative to a key. The music may be labelled as C major, and that is fine, but the chord symbols are always relative to each individual root. Don't expect the intervals of the chord symbol to be diatonic to the key signature of the song, the intervals to be read relative to the chord root.


'...is going to be different depending on the key' - not really. Any chord in any key will always contain the same notes - and all called by the same names.Regardless of whatever key it's found in.

What you allude to is your Fmaj9♯11 happens to have a root of F. It will, it always does! But in your scenario, it happens to be found in a piece in key C. If that piece was in key XYZ, it would still have the same notes!

Let's look at the chord itself. F A C -maj. triad. maj.7th is E. Maj.9th is G. Then the red herring. ♯11th using F as root, is B♭, sharpened. So it's B♮. In any key, that's what constitutes that chord.

To try to answer your final question, there's no B♯ in it, because there never was, and never will be! B♯ is not the ♯11 from root F. The 11th from root F is B♭, so when it's sharpened, it becomes B♮. Going to B♯ (sounding like C) is too great an interval, and in any case, would be a pointless addition to the sound of that chord.

So, to summarise: every chord is taken on its own face value, and its intervals are worked from its own root name, and has no reference at all to whatever key the piece is in. Note, on some instruments - guitar in particular, one or two notes may well have to be omitted to enable fingering and voicing to be taken into account - but that's for another question!


Your thoughts are in the right place but you are over thinking it. There is an algorithm for building chords and that is independent of the Key that the cord is being used in. We always refer to the notes of the chord relative to a major scale starting on the root of the chord. As an example when we build the minor triad we don't say (1, 3, 5) on the minor scale, we say (1, b3, 5). The b3 is necessary since we are using the major scale as a reference (like a ruler).

Picking the letter names and accidentals can seem tricky and unnecessary since you will have accidentals in the "Major scale" being used that may be flattened and hence removed. But again, this algorithm makes the process simple once you get used to it. On the other hand the formulas for chords when expressed as degrees or intervals are the same no matter what key you are in, making them very easy to use.

Example 1: Build the A min 7 chord (A-7). The formula in degrees is (1, b3, 5, b7). Starting from the A maj scale (A, B, C#, D, E, F#, G#) we take (1, 3, 5, and 7) = (A, C#, E, G#) and flatten the 3rd and the 7th. Since these are # this amounts to making them natural, (A, C, E, G). This is in the key of C and A is the relative minor of C maj. But the chord is also inside the Dorian and Phygian modes.

Example 2: Build Fmaj9#11. Based on my references this is built on the Maj 7th chord so the formula is (1, 3, 5, 7, 9, #11). We usually do not play the 5th. Take these notes (without accidentals) out of the F Major scale (F, A, C, E, G, Bb). Now apply the alteration to the 11th (Bb). We sharpen it which makes it natural (i.e. cancels the flat). The final result, (F, A, C, E, G, B). Notice that once again, this is in the key of C major. The diatonic mode on Fa, Lydian, has a sharp 4th in it. This does not mean that we build the chord on F Lydian (though no one would fault you for thinking of it this way). You could build it on C in the key of C, requiring an accidental that is out of key.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.