Good day! I'm in the process of creating a songbook of Civil War era-ish songs and hymns, and am using the chord numbering system (1 4 5), which seems to be working. I've gotten mixed reviews on using a numbering system rather than regular chords. Ironically, beginners tend to love it, while advanced players don't.
My question lies with songs in minor keys. I wasn't able to find any minor key songs in the song repertoire on this site (I might not have looked in the right place), and I was wondering if anyone has had any success with numbering songs in minor keys.
I believe you are speaking of the “Nashville Number System”, developed in the late 1950's as an easy way to indicate chord changes using the 'degree' of a music scale. No matter the key, you number the degree of that scale - Do = 1 (I), Re = 2 (II), Mi = 3 (III), Fa = 4 (IV), etc. It is movable from key to key. Many use Roman Numerals.
To indicate a minor (outside of the key), the number would be followed by a lower case 'm' or a dash '-'. For example 4m (or -), 5m (or -). This is the standard way of indicating a minor.
Hope this helps,
I fudge a little on minor key songs. Below is a song set for playing in A minor. The first chord, [6m], is played as an A minor and the next chord  as G and that  as E seven.
If you want to play it in B minor, you would capo on the second frett etc.
Playing this in D minor would involve playing as key of G as the  chord with the [6m] starting off played as D minor.
A bit confusing but it seems to work.
What child is this [C]
1 [6m] What child is this, who,  lay to rest,
on [6m] Mary's lap, is  sleeping
Whom [6m] angels greet with  anthems sweet,
while [6m] Shepards  watch are [6m] keeping
I think I should clarify my misunderstanding - are you asking about minor key songs, not an occasional minor chord played in a major key?
If so, then the minor key is the actual scale, you don't indicate the minor chords any differently - it is just part of the minor scale.
Em scale example: Start on your key note (which is Em - chord 1) and go up the scale. For Key of Em, the 1-4-5 chords are Em, Am, Bm. They are played within the scale:
Em - this is the 1 chord
F# - this is the 2 chord
G - this is the 3 chord
Am - this is the 4 chord
Bm - this is the 5 chord
C - this is the 6 chord
D - this is the 7 chord
Em - this is the 8 chord
Ah, music theory - the bane of our existence!
My earlier comment about playing minors out of the G position was off one step. I should have said I play E minor songs using E minor as the 6 minor chord.
To me the easiest and most clear would be to notate all minors using a lower-case m, and all flatted chords using a lower case b.
The Toneway notation for Little Sadie, which is a minor-key song, notates the 1 as '1m' and the 7 as '7b'.
Toneway notation for Red Rocking Chair uses 1m and 3b.
Wayfaring Stranger in a minor key and has a 1m, a 4m, and a 7-flavored 5. It's simplified in the Toneway book but you can see it in the StrumMachine by putting it in Am and then writing it out with numbers for the chords.
When I notate chords for a song in a major key that has a 6 minor, I always put 6m, even though it is can be assumed that the 6 will be minor.
The 2 chord is a little more troublesome. Typically I do NOT put anything next to the (major) 2 chord, even though the 2 is naturally minor in a major key, because I go with the assumption that all chords are major unless notated otherwise. And also because the 2-chord in a major-key song in the world of oldtime and bluegrass is usually a major 2, because it's usually operating as the 5 of the 5 (as a leading chord to the 5 chord) not as the 2. Anyhow. I just put a 2. Unless it IS a minor 2 in which I put 2m. But depending on your audience, you might want to put 2M there, so everyone knows it's a major 2. For an example, see Redwing, where the 2 chord is most definitely major and is functioning as the 5 of the 5 chord.
Also be alert for when there's 7-flavored chord (not a 7 chord). For example, a 5 chord in the key of C that (in some particular song) should be played as a G7. For those I use a little superscripted 7 above and to the right of the 5 chord number. I can't show it here but you get the idea.
Thanks for your interesting question! I enjoyed thinking about it. I hope this helps. -Jessica
Ironically, beginners tend to love it, while advanced players don't.
Yes! We found the same true overall with teaching this method. Beginners have the least trouble. The more one 'knows', the harder time one often has learning this easier way. Perhaps because it is simpler and more intuitive? I.e., those that 'know' need to unlearn in order to learn.
Ironic indeed, and perhaps hints at answering a deeper conundrum as well: How do really smart people end up doing really stupid things?
My question lies with songs in minor keys.
How about just adding 'm' to the chord numbers: 1m, 4m, 5m. Or just put in the heading somewhere a note that all chords are played minor, if that is the case.