In the process of writing The Jazz Standards Progressions Book Series I realized the need to express a very common harmonic event with a new symbol. So far we had solid and dotted arrows and brackets to express II-V relationships and their resolutions. However there isn’t any symbol to show a Major 7th chord that becomes a minor 7th chord. It happens so often that I started using a symbol to show this harmonic event in my analyses. I just makes sense to me to show this along with brackets and arrows. In my opinion it adds an important quality to the overall visual representation of the music and what is going on harmonically.
At mDecks Music we came up with this new symbol: a headless straight arrow, as shown under the number 3 in this image:
In this case the CMaj7 turning into a Cmin7 is analyzed with this new symbol we call “TO MINOR”.
Here’s the page dedicated to Arrows & Brakets in The Jazz Standards Progressions Book:
A cool way to illustrate this is the song “Afternoon in Paris”. Here you can see the full harmonic analysis, chord scales and complete arrows & brackets analysis, including our new symbol: TO MINOR