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Can a chord contain both the C and C♯ notes? Or do you always have to use D♭ rather than C♯ in a chord that already contains the note C?

I'm guessing the answer is no, both C and C♯ should not be allowed - but I do see a lot of inconsistency on the web with what enharmonic is used to describe a chord.

For instance, take the A♭m chord. I'm pretty sure it is correct that this chord contains the notes A♭, C♭ and E♭ ? In many places I look online, they say the C♭ is a B. But I don't think that is right, because in the A♭ major scale, the B is flat.

So therefor, going back to my question, a chord in the key of A♭ can never contain a "straight" B note. The B must always be one of B♭, B♯ or B♮. And if you're talking about a note that represents the 3rd, then that note must always start with 'C' - and therefor the minor third in Ab major can never be described as B.

Correct?

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  • The diatonic third in A♭ is always going to be some kind of C, because B♭ is already the diatonic (major) second and, as mentioned, when naming chords in a diatonic scale each note must be assigned a different name. A♭m will use the minor third, C♭ (which is enharmonic with B), while A♭M will use the major third, C.
    – Rein Henrichs
    Aug 29, 2011 at 17:26
  • This question shows an example of such a clash between two notes in the same octave. music.stackexchange.com/questions/24030/…
    – Rosie F
    Oct 10, 2018 at 6:15

12 Answers 12

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In classical Western music theory, each diatonic scale contains seven notes, and each of the notes must be assigned a different note name. (So one also does not write CX for the D in the C major scale.)

In non-equal temperament, C# and Db may in fact be two different pitches, and a diatonic scale that contains a C must not also contain a C#.

In more modern music theory, uses of polytonality and non-diatonic scales in composition, especially the chromatic scale with 12 tones and the diminished and bebop scales with 8 tones, make it impossible for a scale to contain only notes with distinct note names. That and the widespread use of equal temperament (so that C# and Db are indeed enharmonic equivalents) makes it slightly more acceptable to refer to the third note in the ascending Ab minor scale as a B; though perhaps this practice is for the sake of players (especially piano players) less trained in music theory that thinks of sharps and flats as only modifiers to change from white keys to black keys.

I do think the vast majority of musicians performing Western music will prefer you spell Abm as Ab Cb Eb, and not Ab B Eb.

But going back to your original question: I don't see why not (theoretically). The presence of a minor second or a minor 9th is a big aesthetic no-no in a lot of chord-voicing traditions, but that rule may not be so hard and fast. In theory, the same notes may even be interpreted differently functionally by fitting them over different scales. For example, the notes C-E-G-Bb-D# spell the usual C7+9 chord. But reading the D# as an Eb, those are the root, 4th, 6th, 8th, and 3rd notes of the C diminished scale.

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    The question is not if a minor second or a minor 9th is a problem, because they would entail a Db in a chord with root C. The question is if an augmented prime (or an augmented octave), i.e. a C# will occur or not.
    – Matt L.
    Sep 28, 2014 at 19:44
  • @MattL. assuming equal temperament, the two are equivalents as far as the harmonic contents go, so aesthetic objections to minor 9 apply equally to augmented octave. My third paragraph already addressed the issue of "chord spelling": in short, yes, they do occur, and for good reason. // In unequal temperament, the two notes are different, so if it is really a C# you have to spell it like that, and not as a Db.
    – Willie Wong
    Sep 29, 2014 at 11:24
  • This does not answer the question. The OP was at pains to specify "the C and C♯ notes? (as opposed to containing C and D♭ notes)". Min 9 is not the same as aug 8ve. In this OP's context we may not pretend they're equivalent, because the OP concerns harmony, NOT temperament.
    – Rosie F
    Oct 1, 2018 at 15:26
  • @RosieF: did I not address that in the first and third paragraph? The first paragraph addresses specifically the classical western tradition of requiring different note names for tones in a scale, and the third paragraph addresses specifically the lack of this need in modern music theory where a scale may contain more than 7 notes.
    – Willie Wong
    Oct 1, 2018 at 15:31
  • You don't have to have equal temperament to have enharmonic equivalence. Any 12-tone temperament will do.
    – phoog
    May 6, 2021 at 12:36
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I can think of at least one example where I encountered a C and C# conjoined. In Béla Bartók's Nine Little Piano Pieces, you'll find them in the Menuetto from measure 10 on.

It would be natural to find more of these in Bartók, especially the pieces using polytonality. Other composers using polytonality like Stravinsky should also have them. So, look for composition of the early 20th century using polytonality.

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Check out Chopin's etude op 10 no. 2 in A minor. He uses this kind of device all throughout. In fact, it's just what you're taking about, a C and C# at the same time.

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You are correct that Ab minor must contain a Cb, not any form of B (even though Cb and B are "enharmonically equivalent", Cb is the correct spelling here).

However, there are contexts in which two different versions (e.g. sharp and natural) of the same base note can sound together. When this occurs, it is called a "chromatic contradiction," or a False Relation. Since this won't ever occur in a single diatonic scale, the two clashing parts must come from different scales. One place this might occur is in when one is playing a descending melodic minor scale, while another is playing an ascending minor scale.

This technique isn't even limited to modern classical music. It goes back as early as the Renaissance Era. Here's what it sounds like.

I believe that "blues notes" might work like this sometimes as well, where you have a major chord in the accompaniment, but with a minor third in the melody.

This question contains a picture of an example where this occurs in Chopin: What does this split stem notation mean?

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In jazz, a sharp 9 chord is often spelled with both thirds emphasizing the bluesey major/minor sound thus A7+9 = A C# E G C though the last C would technically be a B# according to the rules of western harmony.

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    A 7#9 chord doesn't have both thirds. It has a major third and a sharp 9. The sharp 9 is enharmonic with the minor third but functionally quite different.
    – Rein Henrichs
    Aug 30, 2011 at 20:03
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    @ReinHenrichs: correct. There is something to this answer though: you can voice A7+9 with both the b9 and the #9. There you have A, Bb, B#/C, C#. I would prefer to spell it A - C# - G - Bb - C, thus having both C and C#. This is really a sign of the limitations of our notation system, in my opinion.
    – Gauthier
    Apr 22, 2013 at 18:09
  • @Gauthier: The issue is that the 7#9 chord is often considered to be constructed from the 7th mode of the (ascending) melodic minor scale, but Bb melodic minor has a Db rather than a C#.
    – Rein Henrichs
    Apr 22, 2013 at 18:49
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    Agreed. And having a Db instead of a C# in a A7 variant of chord feels... urk. This is what I meant with limitations of the system. You can see A7+9 as a chord with the third, the seventh, a minor ninth, and an augmented ninth, then come up with one spelling. Or you can see it as a set of tones from Bb minor melodic and come to another spelling. There are several ways to look at it, and they are not very consistent. It is even worse when you start using things such as diminished scales (on A7b9. Too many tones!) or whole tone scales (too few!).
    – Gauthier
    Apr 23, 2013 at 13:49
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Well, sure. As a chord is simply any number of notes defined in terms of their interval from a "root" note, a chord can have any two or more semitones in it. A lot of contemporary composers such as Eric Whitacre play around a lot with dissonant intervals and "cluster chords" involving minor-second intervals like C/C#.

More realistically, it would be rare to see both a C natural and a C# in the same chord, notated as such. This is primarily because the notes would take up the same line or space in the staff, so it would be difficult to sightread and could be impossible to notate properly if there's a D or B in the chord as well (as in the aforementioned cluster chords). However, C# and Db are enharmonic (same note on the piano keyboard), so you may see a C and Db in the same chord. In the key of Ab, an Ab major triad with the fourth added (not a suspended chord, but an add4) would have both of these tones, and in the contemporary climate of music composition it wouldn't be that odd to hear.

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For instance, take the A♭m chord. I'm pretty sure it is correct that this chord contains the notes A♭, C♭ and E♭ ? In many places I look online, they say the C♭ is a B. But I don't think that is right, because in the A♭ major scale, the B is flat.

A minor triad is a minor third then a major third. A♭ to C♭ is a minor third and C♭ to E♭ is a major third. A♭ to B is an augmented second and B to E♭ is a diminished fourth. They'll both sound the same when you play them on a piano or guitar, but if you write them down the second one would be considered wrong.

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Yes. (And it's even consistent with common-practice harmony, not that you're obliged to stick to that.) For example, in D minor, you may have C# in the harmony (the third of the dominant), and also C as a melody note (the seventh degree of the descending melodic minor scale).

Here is an example. (Bizet, L'Arlesienne suite no. 1, mvt. 3 (Carillon), b.5 and 7 of the Andantino section.) The key is C# minor, with the notes being B and B#.

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Neutral intervals are usually voiced with the major and the minor simultaneously on chromatic instruments that only have semitones (fretted instruments, most valved winds and keyboards without pitch bending).

Eg. an A neutral consists of an A, a C half-sharp (it's the quartertone between C and C#, for the notation imagine the # but with only one vertical instead of two) and an E. On a piano this will be voiced with A, C, C# and E. Harmonies with neutral thirds and neutral sevenths are found in music based on scales found in Africa. And if I mention neutral sevenths, of course a D neutral is another example for C and C# to be present at the same time. This would be voiced with D, F, F#, A, C and C#.

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The chord could have a Chromatic non chordal note that has a C#. If say for argument sake we are G Major and we go from IV to V we may have a non chord note that forms the baseline C-C#-D

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YES, but if you RE-NAME the C as B#. Yes B# is the enharmonic equivalent of C. But because the C is assigned to C# we have to bump up the B to take the place of the C. It's a linguistic wordplay game but it is necessary for the rules of the game we have chosen to play.

examples:

C#maj7 = C# E# G# B#

A#m(add9) = A# C# E# B#

F#maj7#11 = F# A# C# E# B#

if you believe it is unruly or sloppy to use any letter name more than once, the answer is NO!!!

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  • This does not answer the question. The OP was at pains to specify "the C and C♯ notes? (as opposed to containing C and D♭ notes)".
    – Rosie F
    Oct 1, 2018 at 15:18
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If your world view contains a system of harmony that tells you what you MAY do, you'd better follow its rules. If it contains one that attempts to describe what IS done, work out what you mean by such a notation. If you have a reasonable answer, it's good!

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