I've been writing my own songs for a while now and I have a question.

How do you know which chords belong together in the same key? Of course I can hear which chords sound right together and which don't, but there must be a better way of coming up with chord progressions other than just hap-hazardly stringing chords together until I find some which sound right.

I've often seen that roman numeral thing used when describing chord progressions (I-IV-V etc), but have never really understood what these mean.

Is there a book or something which could help me with this?

There's no quick way to answer this question properly. By way of a very brief explanation, the Roman numerals denote each degree of a scale upon which a chord is built. In a major key, you have seven chords:

I - Major
II - Minor
III - Minor
IV - Major
V - Major
VI - Minor
VII - Diminished.

Taking the key of G as an example, looking at it diatonically (like the traditional major and minor scales, and not chromatically, which is where the scale goes up in semitones, which in guitar terms is just going along one fret at a time) the chords would be:

I - G Major
II - A Minor
III - B Minor
IV - C Major
V - D Major
VI - E Minor
VII - F# Diminished

So if you establish you're playing in the key of G, you could express a G Major, A Minor, C Major chord sequence very simply as I, II, IV.

There's a lot more to learn about this. If you're based in the UK and really want to get into your theory and applying it to a guitar, you wouldn't go far wrong with doing your grades: http://www.registryofguit...guitar.htm
[Edited 1/27/08 9:34am]
[Edited 1/27/08 9:37am]

Rowdy said:

Thanks - that's really helpful.

Rowdy said:

shouldn't that be F# diminished?

MattyJam said:

No probs - FYI I made a tiny edit to my initial post - I forgot to add "7 chords" before the first rundown of numerals.

coolcat said:

yes

#edits that too#

So is there a similar thing for minor keys?
[Edited 1/27/08 9:39am]

MattyJam said:

Yes, but it's more complex again because you use 2 scales - the melodic and natural minor scales, which in turn means more chord choices.

I'd really suggest looking at grades - it's a staggered progression for learning all of this stuff. When you reach Grade 8 (I think), you'll also find yourself as a qualified teacher, which is a nice goal to aim for.

I have thought about doing grades. Have you done them? Do you have to start from Grade One or can you enter yourself at any level?

Is there a roman numeral chart for minor keys like the major one you posted above?

MattyJam said:

I never did my Grades - I researched them heavily a few years back after when I was offered a teaching job, but in the end I decided to focus on a steadier line of work. You can enter at any level, so if you're an advanced player, there's no need to pay out for doing Grade 1 for example.

Minor key numerals - it's more complex - you have some flats to consider:

I - Minor
II - Minor or Diminished
flat III - Major or Augmented (Augmented chords are normal major chords, with the third note half a step higher)
IV - Major or Minor
V - Major or Minor
Flat VI - Major
VI - Diminished
Flat VII - Major
VII - Diminished

E Minor for example:

I - Em
II - F#m, F#Dim
flat III - Gmaj, Gaug
IV - Am, Amaj
V - Bm, Bmaj
Flat VI - Cmaj
VI - C#dim
Flat VII - D maj
VII - D#dim

Rowdy said:

So going by that, F minor (which has Ab, Bb, Db, Eb) would be:

I - Fm
II - Gm
flat III - Ab
IV - Bbmaj or Bbmin
V - Cmaj or Cmin
Flat VI - Dbdim
VI - Ddim
Flat VII - Ebmaj
VII - Emajdim

Is that right? I have a feeling I messed up with the diminished ones.

MattyJam said:

I - Fm
II - Gm, Gdim
flat III - Ab, Abaug
IV - Bbmaj or Bbmin
V - Cmaj or Cmin
Flat VI - Dbmaj
VI - Ddim
Flat VII - Ebmaj
VII - Edim
[Edited 1/28/08 12:33pm]