Once again we are dealing with slash chords in descending bassline progressions. This time also starting from minor and minor 7th chords. We will learn, that it can sometimes be better to write chord names in a way that doesn't describe the chord in the most correct way but therefor makes it easier to read and understand in a certain context.
Descending bass starting with a major chord
Major triad with 3rd as lowest tone
You may remember the G/B chord ("G over B", G major chord with B in the bass) from the first lesson on slash chords
The chord diagram shows one of many possible chord shapes for a G/B on the guitar.
Here is a lesson with a video to play along with, where you can practice this chord progression with various chord shapes and in several keys: chord progressions → I-Vover3rd-VIm-IV
Only the bass tone descends
Now we don't descend via G/B. Instead we just lower the bass tone by a half step going from C down to B.
Here are two chord shapes for a C/B chord:
All root tones descend
If we not only lower the bass note itself but all of the C's we can find in our chord shape instead, we'll end up having an Em chord with B in the bass (Em/B). That may be a little bit confusing, causing the player to search for a whole new chord shape instead of just moving the few relevant tones.
In practice a trick is often used: we pretend starting from a Cmaj7 chord shape, now lowering the bass note by a half step. We name the chord Cmaj7/B ("C major seven over B") regardless of the fact that we have no more C in the chord at all by now.
That results in faster reading and probably exacly the chord we want to hear. At least for most of us guitar players the following two lines mean exactly the same:
Strictly speaking the C/B chord from above could even more likely be written as a Cmaj7/B chord, because it contains all the notes of a Cmaj7. But normally it isn't necessary to note the function of the bass tone (here: maj7) on the left side of the slash.
On the next page we are starting with minor and minor 7th chords...
Descending bassline starting with minor or minor 7th chords
Dm → Dm/C
Let's have a look at the following chord progression with descending bassline:
To change the Dm to a Dm/C, we have to replace the root D in the bass by a C.
It would be correct to call this new Dm/C chord a Dm7/C, because the new bass C is the 7th of Dm. But nomally we can ignore the function (interval) of the bass tone in the chord name on the left side of the slash. Writing Dm7/C is usualy done for a different reason...
B half diminished (Bm7b5) can also be seen as Dm/B. That means only the bass tone is moving in the first three bars.
Dm7 → Dm7/C
Now starting from a minor 7th chord:
Again the same thing is happening. The root D is going to be replaced by a C. But when we take a closer look at the resulting chord shape, we see that there is no more D at all in the chord!
Strictly speaking our new slash chord is not a Dm7/C, but F/C - a F major triad (with the tones F, A and C) over C in the bass.
In practice we are just looking at the descending bass tone and therefor we name our slash chord in a way that instantly makes clear what you have to do on your guitar rather than trying to be too precise.
We are writing Dm7/C, because the chord has derived from the preceding Dm7
(even if there is no more D in the entire resulting chord).
It's not always about the most possible accuracy. The goal is to make a player reading fast and not to play needlessly complicated.
Starting from minor, but descending via the maj7
Dm → Dm/C#
If we lower the bass note of the Dm chord by just a half step (from D to C# - the maj7 of Dm), we should lower all D's in the chord to C# (otherwise is may sound terribly dissonant). Now the resultng chord is actually an augmented C# chord (C#aug or C#+). Got it? Not quite clear? Ok, that's why we prefer writing Dm/C#. Coming from Dm you will instantly know what to do (your playing experience will tell you), even if the chord symbol is not really completely correct.
Example chord progression
Actually the same, notated even more correct - but relatively complicated, isn't it?
Finally you can use both variants. It probably takes some time and experience to always chose the right chord name for each harmonic situation.