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Is there a convention about how to name two-note chords? I noticed that software like Apple Logic Pro names two-note chords like this:

  • Db C = Db no 3 ma7
  • C Eb = Cm

So I'm assuming the dynamic for naming two-note chords exists, but for many reasons this specific algorithm feels not complete, like it not being context-aware or not including omitted notes in the name(C Eb could be labeled as Cm no 5th, for example) or not naming other possible names based on inversions and other note orders (F C could be F indeterminate or C sus4 no 5th, but that specific algorithm labels it only as F5).

Is there a standard practice to name two-note chords? Is there literature about the subject? I'm not looking for definitive labels, as I know the name depends on the context, so harmonic relativity like C6 = A-7 (a list of possible names, but for two-note chords) is perfectly fine.

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5 Answers 5

up vote 5 down vote accepted

I don't have a reference to cite, but from your description and my knowledge I believe this constitutes a functional list of two note chords, exemplified as C chords:

Interval    | Notes | Chord name
(semitones) |       |
============|=======|===========
     1      | B C   | Cmaj7no3
     2      | Bb C  | C7no3
     3      | C Eb  | Cm
     4      | C E   | C
     5      | G C   | Cno3 or C5 (power chord)
     6      | C Gb  | Cdim no3

Higher numbered intervals can be considered inversions.

Explanations
The perfect fifth is the most expendable note of any chord and can often be omitted without mention. The reason for this is that it adds very little color or texture to the chord since it is so consonant, and that it is also present as an overtone of the root note. The third, on the other hand, is the most characteristic note of a chord since it determines if the chord is a major or minor chord which is the most fundamental characteristic of a chord. Due to this you prefer to name the two note chord from a third interval if there is one, and if there is none you want to specify the omittance. These are the reasons behind the naming of the chords with intervals 1-4.
The perfect fifth chord (5) has a name of its own ("power chord") and is very well known in rock. Since its special characteristic is the ambiguity of not having a third you don't need to mention the omitted third. If you are not in the rock idiom you might be better off calling it a no3.
Regarding the tritone (6 semitone) interval, I'm not certain how to call it, but I've listed my guess. (Personally, though, I would perceive a tritone interval out of context as being a third and a seventh of a dominant chord without root or fifth. But perception is not necessarily relevant here.)

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Of course there is: Db C is called Db + a major 7th, C Eb is C + a minor 3rd, and so on...

As Einstein said: Make things as simple as possible, but not simpler.

So, if you want to have names for two-note chords (aka intervals) instead of bigger chords with missing notes, I think this is the way to go. Only use the more complex notation if it is relevant that, say, the Db C is coming from a Db maj7 chord.

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I find context is everything with dyads. Within a progression, Db-C could function in a multitude ways. While it could function as a DbMaj7 sans the 3rd, it might also function as a C7(b9), F7b13, Bb-9, Gb7#11, Eb13, Ab11, F#7#11, A7#9, etc. With just two notes, the chords list can get just about endless (especially if you're willing to delve into enharmonics, alterations and extensions).

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A pair of notes can belong to many chords. If we say that a pair of notes is a chord it allows the possibility that there may be a third, possibly unheard note that is the root note of the chord. And only the context reveals what that root note might be.

For example, imagine hearing a car-horn sounding a minor 3rd. When I hear this I consider the two notes to be the 3rd and 5th of a Major triad. I've mentally constructed the root of the chord, even though I can't hear it. Other people listening will hear the same two notes as the 1st and 3rd of a Minor triad. It's the same interval we're hearing, just our internal context that's different.

Conventional music theory describes two-note intervals unambiguously relative to the lower note.

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There are some systems for that. The easiest coherent system is to just write down the two notes, because it often takes the fewest space and you dont have to 'think' (use minuskels because they stand for tones instead of chords):

c/e, d/f …

but C/E = e, g, c (first inversion of C)

The logical system is based on the function (if any), and therefore just has a limited range of ways to express something, so of the 11 possible combinations with c in it, only 6 have a function and therefore a chord-code:

  • Cm3 = c e♭ (C minor, quint missing)

  • C3 = c e (C major, quint missing)

  • F5 = c f (F powerchord)

  • C5 = c g (C powerchord)

  • A♭3 = c a♭ (A♭ major, quint missing)

  • Am3 = c a (A minor, quint missing)

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