Chord Slide Rule
TL:DW; Make your own slide rule for going to crazy jazz chords and knowing what to do with them!
This has been a long journey!
Remember how I’ve been making these wheels of chords, based on the Circle of Fifths? And (in recent videos) I’ve shown how I tried overlaying another wheel, with cutouts first for all the chords that fit within a key (easy, they’re just repeats of what’s in the same vertical slice) and then for the new chords that aren’t in the key?
It all got very simple, and gave me this (it’s nice when that happens).
Print this out, cut and fold it until it’s a slide rule. This is your Chord Slide Rule. The moving bar contains all the chords you could ever want. Basically, all the chords (at least, the major and minor forms, plus major sevenths for Mixolydian mode).
The sliding overlay tells you a bunch of useful things. Firstly, it’s organized into slots (horizontal positions) with the modes written on them. Start from that note and you’re in that mode when using those notes shown in the vertical slide. This also shows you what the chords are, except it’ll show a minor chord in the Locrian slot. That’s true enough but you’re meant to leave out the fifth, which isn’t present in the Locrian mode. Also, for the Dorian, Phrygian, Lydian and Mixolydian modes, it’ll tell you which slot to find a characteristic note indicating which mode that is. For instance, Dorian uses a minor third, but what note makes that different from Aeolian? The major sixth: which is shown in the Locrian slot (in D Dorian, that will be a B natural). This alone is handy.
But there’s more: the Locrian and Lydian slots (interestingly, the slots with a diminished fifth) have arrows on ’em. Locrian points right, Lydian points left. They’re marked ‘New Note’. What this means is, if you went one step sideways into a new key, this would be the new note that wasn’t present in the first key. It tells you what it is, right away. If you move the slide rule over, the other arrow shows you what note you just lost in leaving the original key. So you get to see both which notes are being added, and which notes went away.
But there’s more! Because there are additional slots cut into the slide rule. For any key, you can see not only the chords that belong in that key, but which chords are available in adjacent keys! It’s shown right there. The farther left or right you go, the more out-there the chord change will seem. If you stick in the same general area, the new chords will make sense relative to each other. Or you can change keys entirely by sliding the rule: but you can get a lot of mileage out of exploring the side-chords without leaving the key you’re in. What’s under the blocked-out areas? Copies of the chords already available to you in the key you’re in. Can you go farther to the side, beyond what the slide-rule shows? Sure, and it’ll sound very jazzy and abstract. If you go off the edge, wrap around and come in the other side of the slide rule, like it was a loop (or the wheel that this concept started out as).
You can treat chords, including jazzy modulations, as positions of the slide rule. You can find chords to lead you to key changes (like C major to D major for a big finish, or to B major for an unusual transposition) by seeking chords that ‘walk’ along the circle of fifths to get you to the new key. You’ll see how many new accidentals you have to navigate (two for Cmaj to Dmaj, or five for Cmaj down to Bmaj) and every step of the way you can see what the new note is and which note you lost out of the previous key. For instance, Cmaj to Bmaj means you’re adding F#, Db, Ab, Eb and Bb, and the notes that go away are F, C, G, D and A… in order, if you walked chord by chord along the circle of fifths to do it.
Pretty cool! And you don’t have to know any of that to use it for making up chords and melodies. The vertical slot is the notes (and chords) within the key, and going to the side gives you different chords which will want different notes to go along with them. Slide the slide rule to see which notes those are: if you’re a guitar player who’s familiar with the shape of major or minor scales on the neck, this will show you both where your scale shapes live on the neck, and which note you start on to be in the desired mode.
This isn’t everything music theory has, but it’s a damn fun music theory toy, and I hope you enjoy it as much as me. :)
This is made possible by Patreon: the freedom to study what I wish is what produced this. Thanks to everyone listening… and especially, those who’re helping me keep doing this stuff as a full-time job. No, YOU’RE awesome :)
Oh, one more thing: Airwindows fan Aykut Cirik thought it would be a fun idea to make a webpage that works like the Slide Rule, so you can use it on your phone. So as long as the link holds, you can go to https://www.trinity.be/airwindows_chordsliderule/ and have a quick reference to the Slide Rule as a webpage. Thank you, Aykut! :)