Teaching privately, I come up will all kinds of musical ideas and new approaches as I answer students’ questions. On occasion I dream up a new way to explain something if a student is not understanding the concept initially. Here’s a new approach for you concerning a cool, slightly angst-filled chord that I use all the time, a “half-diminished.” I use them quite effectively in my YouTube videos of “Brother Can You Spare a Dime” and “Easy Virtue.”
The concept: In a major key, combine the ii chord with the key’s leading tone. Voila — you have the key’s “half-diminished” chord. For example: In the key of C, play a Dm chord, and then add a B note to it. This is called a Dm6 chord (B is six scale notes above D) AND it’s called a B half-diminished chord (B minor7-flat5). They use the same notes!
If you don’t know, the ii chord is the minor chord built on the second note of a major scale. The leading tone is the seventh note of the scale, “leading” to the tonic, i.e., the first note of the scale.
Try out these half diminished chords. They are all workable on the guitar:
Key of C: Dm, add B note
Key of A: Bm, add G# note
Key of G: Am, add F# note
Key of E: F#m, add D# note
Key of D: Em, add C# note
What to Call It: What a guitar player may call the half-diminished chord in the key of C — Dm6 or Bm7(flat5) — is open to discussion. Even with music degree training and knowing what academicians would say about the two names, when I play I think Dm6 more often than Bm7(flat5) because it is easier for me to process in the moment. I know Dm chords all over the neck. I know I simply need to add a B note to it and I’ll have the chord I need. There are B notes right next to your Dm fingerings all over the neck. Go find some of them!
A third name for this same chord is: “Dm/B” — said out loud it is “Dm over B.” Play a Dm somewhere on the neck and find a B note that you can reach on one of the bass strings. There’s your half-diminished chord!
A Sub for G7: These can substitute for a dominant 7th chord. Try resolving a Dm6 [Bm7(flat5)] to a C chord. It works just like a G7 to C because the dissonant “tri-tone” interval of B-F is in both chords.
Minor Keys: In a minor key, the “half-diminished” chord IS the ii chord. In other words, in the key of Am the half-diminished chord is the same Bm7(flat5) you used in the key of C major, where it is the VII chord, built on the seventh note of the scale.
It works beautifully as a lead-in to the dominant 7th chord in a minor key. In Am you have: Bm7(flat5) to E7 to Am. You’ll hear it continually in my version of “Brother Can You Spare a Dime.”
To come up with useful fingerings you may still think of this as a simple Dm with a B note added.
So, play a Dm chord anywhere you know it on the neck, and add a B note to it: as simple as the open second string, or anywhere else you can reach it.
Summary: If this peaks your interest, I’ve written a couple of other articles about half-diminished chords on this website. Check them out.