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How do I establish whether a 1b3b7 is half dim or minor?

Active Member
Joined: 10 years ago
Posts: 10
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So I got a chord which consist of ACG= 1b3b7 = AHalfDim OR Am.
Which is it?

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Joined: 19 years ago
Posts: 4933

That depends on context.

I'll give you four general rules in order for naming chords in situations like that...

1. A chord name describes a HARMONY, not a fingering. If any other instruments are playing at the same time, you have to consider their notes too - if the bass player (or anyone else) is playing an E note at any time during your chord, it's Am7. If they play an Eb, it's Am7b5 (the generally preferred name among publishers at the moment over A half dim). You might also discover other prominent notes that should be included - if it's an ensemble piece, you have to consider all the notes being played, and determine which ones are important enough to be included in the chord name.

2. If that doesn't get you a clear answer, map out the root motion of all the chords in the piece, and the general types of chords (major, minor, dominant). Look for a recurring pattern, follow the same logic. For example, if your mystery chord fits into a progression like this:

Gm7 -> C9 -> Fmaj7 -> Cm7 -> ? -> Bbmaj7

you've got a minor-dominant-major (ii-V-I) followed by a minor, ?, major. In this situation you may be looking at an F9 chord voiced without TWO notes: F-A-C-Eb-G. Search the other instruments for an F, consider how the music "feels" at the moment (is it a point of tension?) and see if this, or any other alternative, makes sense.

3. Our experience of music depends heavily on context. If it's a solo piece, or if no other instrument fixes the chord identification by playing an E or Eb during the chord and you don't have a clear root progression, look to see what recent chords contained E or Eb. If you went to the mystery chord from Cmaj7, your ears will still "hear" the E, and it's Am7. If you went to it from something like Abm, you'll "hear" a m7b5

4. If none of that gives you an answer, the simplest name is usually the best; go with Am7.

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Active Member
Joined: 9 years ago
Posts: 13

I agree pretty much with the above. From a theoretical standpoint, you would need more context.

Moreover, from the notes you described - A-C-G, without any context, you could come up with a number of things, including a C6 with the same notes as an Am7 (I also agree that if you play the A-C-G, without the E in there, your ears are likely to fill that in as a perfect 5th, so it will sound like an Am7, so if you want to make it half diminished, you will need to sound out the flatted fifth (tritone) - the bE, which has an unmistakable effect on the chord.

It is all about context, but unless you know that the 5th is doing to be diminished, I'd go with the most simple explanation - Am7 (or maybe the C6).

Active Member
Joined: 9 years ago
Posts: 11

So I got a chord which consist of ACG= 1b3b7 = AHalfDim OR Am.
Which is it?

I think that this is not a chord. This is a chord voicing.

Am chord consists of three notes A-C-E. 1-b3-5
Am7 chord consists of four notes A-C-E-G. 1-b3-5-b7
Amin7b5 chord consists of 4 notes A-C-Eb-G. 1-b3-b5-b7

The chord voicing that you have found consists of 3 notes 1-b3-b7. It can be used for all the chords that you have mentioned.
You can use it for Am, Am7 or Amin7b5.
if you use it for Am, you will add a b7 to the chord.
If you use it for Am7, you will not have the 5th of the chord which is not considered an important chord tone.
in the case of Amin7b5, you will not have the b5 which is considered an important chord tone

Some things to consider while using voicings:
The melody of the tune, or the solo of the improviser that are designed to accompany. Don't use tensions that clash with the song’s melody or can distract the soloist.
When you are connecting voicings one after the other there are endless possibilities. It depends more on the voicing before and the voicing after.
I hope that this will help you.