Step by step

Us­ing Ro­man nu­meral no­ta­tion to de­scribe chord pro­gres­sions

Computer Music - - Make Mu­sic Now | Easy Guide -

1 Let’s start off in tra­di­tional fash­ion by look­ing at the C ma­jor scale – seven notes from C to B, played on the white notes of the piano key­board. When talk­ing about scales such as this, we re­fer to the notes not just as notes, but as ‘de­grees’. So we can also say that there are seven de­grees in a ma­jor scale.

2 This is what it looks like when we num­ber these de­grees from 1 to 7 us­ing Ara­bic nu­mer­als. The root note of C takes the num­ber 1, D is num­ber 2, E is num­ber 3 and so on, up to B as num­ber 7. But what hap­pens when we har­monise the ma­jor scale by adding al­ter­nate notes from the scale to each de­gree to make three-note chords, or ‘tri­ads’?

3 Here’s where the Ro­man nu­mer­als start to be­come use­ful: if we re­place the Ara­bic nu­mer­als with the Ro­man equiv­a­lents, we can use up­per or lower case Ro­man nu­mer­als to de­note whether a chord is ma­jor or mi­nor. This frees us from the con­straints of the cur­rent key, al­low­ing us to con­struct a for­mula for a chord pro­gres­sion that works in any key.

4 Let’s il­lus­trate this a bit more clearly by look­ing at a ba­sic pro­gres­sion in the key of C ma­jor. We’ve got the chords C ma­jor, F ma­jor, G ma­jor and C ma­jor. These are all chords taken from our har­monised C ma­jor scale, mak­ing it what’s known as a ‘di­a­tonic’ pro­gres­sion – all the notes in all the chords are taken from the C ma­jor scale.

5 Be­cause the chords are di­a­tonic – they be­long to the har­monised scale – we can swap their names for Ro­man nu­mer­als. So our tonic chord, C ma­jor, is go­ing to be the I chord. F ma­jor is the fourth chord in the har­monised scale, so this will be­come the IV chord, while G ma­jor, by the same process, be­comes known as the V chord, mak­ing this a I - IV - V - I pro­gres­sion.

6 But what if we now switch the key from C ma­jor to, say, D ma­jor? We still have the same pro­gres­sion, but the chords that we’re play­ing are go­ing to be dif­fer­ent be­cause we’re now in a dif­fer­ent key. Here’s what the har­monised D ma­jor scale looks like, with our di­a­tonic chords la­belled with Ro­man nu­mer­als.

7 Note how the pat­tern of ma­jor, mi­nor and di­min­ished chords is the same for D ma­jor as it is for C ma­jor. So ap­ply­ing the for­mula for our orig­i­nal pro­gres­sion, the I chord of D ma­jor is D ma­jor, the IV chord will be G ma­jor and the V chord will be A ma­jor. So in this key, our I - IV - V - I pro­gres­sion is played as D ma­jor, G ma­jor,

A ma­jor and D ma­jor.

8 How about some­thing a lit­tle bit more F# com­plex in, say, ma­jor? Here’s a F# Bbm Ebm pro­gres­sion that goes - - -BAbm C# F#. - - When we match these chords F# up against the har­monised ma­jor scale Abm, Bbm, C#, Ebm, (F, B, Fdim) and la­bel them with Ro­man nu­mer­als, it trans­lates into the pro­gres­sion I - iii - vi - IV - ii - V - I.

9 Let’s now switch to a dif­fer­ent key – how about A ma­jor? The di­a­tonic C# chords for this key are A,Bm,m,D,E, F# G# m and dim. So, if we ap­ply our Ro­man nu­meral for­mula for the pro­gres­sion (I-iii-v i-IV-ii-V- I ), we get the chords C# F# A- m-m- D-B m-E- A.

10 So far we’ve been look­ing at di­a­tonic chords, made up only of notes from the scale re­lat­ing to the key we’re in. But how do we la­bel non-di­a­tonic chords – ones that don’t be­long to the key, like bor­rowed or modal in­ter­change chords, for in­stance? This pro­gres­sion in the key

Ab of C ma­jor con­tains an ma­jor chord which doesn’t be­long to the key of C ma­jor.

11 With chords like this, where the root note has been sharp­ened or flat­tened rel­a­tive to the reg­u­lar di­a­tonic ma­jor scale chords, we place a flat or sharp sym­bol in front of the Ro­man nu­meral for that chord. So since A is the sixth chord of C ma­jor, our

Ab bor­rowed ma­jor chord gets la­belled as bVI.

Up­per case be­cause it’s a ma­jor chord, with a flat to show it’s a flat­tened VI chord.

12 To round off, last month’s Easy Guide, which dealt with modal in­ter­change, fea­tured a chord chart of all the chords avail­able in all of the har­monised modes based on the root note of C. This ver­sion of the chart uses Ro­man nu­mer­als in­stead, mean­ing that it can be ap­plied to any key, not just the key of C.

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