How to determine what key changes are appropriate?

Question

In the month or so until my band get back together I've been working on writing some new material, and want to try and expand how complex my songs are. I apologise if there are a lot of questions - I'll gladly split them up if needs be.

Say I've got a nice little riff/idea in D minor. I'm happy that the relative major of that is F major, how modes fit into a major/natural minor scale, the tonality of the various degrees of the scale, and the concept of the circle of fifths. I also appreciate that a song need not necessarily change key to have a very different sound.

I'm looking at complete changes of key to try and bring a new direction to a song outside of these ideas. So ultimately, can someone explain:

• What keys can I change to from a given key?
• What is the theory behind the potential key change?
• The word modulation seems to by used a lot in similar circumstances. What is the difference between a key change and a modulation?

The more detail the better, as I want to understand the theory behind what I'm doing for myself rather than just follow rules blindly.

Answer 1

a) What keys can I change to from a given key?

In the 21st century, it doesn't matter so much where you go, but how you get there and whether or not you want to nod to classical tradition or ignore it. I'll outline a couple of examples, but rather than make giant lists, I'll say that the key that you aim for should be musically appropriate for the song. If what you're writing needs a drastic change, then pick a drastically different key. I'll outline some techniques below.

As an aside, in the "classical" tradition, the answer to this question depends on what time period you're in as different keys became acceptable as time moved onward.

b) What is the theory behind the potential key change?

The theory you use depends on where you're going. Rather than explain everything, I'm going to suggest a list of terms to look up to learn for yourself:

• Authentic Cadences
• Plagal Cadences
• Deceptive Cadences
• Pivot Chords
• Secondary Dominants
• Mediant Relationship
• Chromatic-Mediant Relationship
• Parallel Minor
• Modal Mixture

Pivot chords, Secondary Dominants, and Chromatic-Mediant Relationships should especially be of interest to you if your are looking for such disparate key changes. The terms I've mentioned above are of course only a small range of possibilites for you to explore.

c) The word modulation seems to by used alot in similar circumstances. What is the difference between a key change and a modulation?

Like I mentioned in a comment above, a modulation is the process of moving from one key or tonal center to another key or tonal center. It is the act of transitioning itself, not the resultant key. A key change is the object being aimed for. Linguistically, you can think of a key change as being like a noun and a modulation as being an adjective that describes the noun. This translation is not literal of course, but it can give a better idea.

Hope that helps.

Answer 2

The common key changes are up a semitone and up a tone. The semitone works well because the root of the old key becomes the maj. 3rd of the new key's dominant chord. As in C maj.: to get to a new key, playing the dominant (5th) chord (Ab or Ab7) of the new key of Db uses the same C note, so there's a sort of continuity giving a smooth change.

Going from C to D involves using A or A7 as the dominant changer, which contains a G that was present in the C chord.

Generally key changes move upwards, so to be different, try going down a semi/tone

Actually you can change to any key, but most will flow better with that new dominant to get into the new key.To even a non-musical listener, going directly into a new key sounds more like 'was that a mistake?'. Some will sound quite drastic, but if that's what the song needs, so be it. Bear in mind the poor singer, who may not have the range to reach the new key !

Modulation is more a temporary key change, shown in the music with accidentals rather than a new key sig.

You can also use the tried and tested II-V-I approach to the new key,where all three are in the new key.

The other ones sometimes used are going to the 4th or 5th of the old key, but these don't sound like a 'proper' key change, as you've only actually introduced one new note into each, e.g. from F to Bb, only adds an Eb instead of the original E, even if the melody line is lifted/dropped by nearly half an octave.

Answer 3

a) often people change to a key that's only one flat or sharp away from the current key. another way to say this is moving around the circle of fifths/fourths

b) the dominant 7th motion down the circle of fifths

c) no difference. key change = modulation

Answer 4

You can go anywhere.

Frequently, when arranging a medley of songs for a selection of singers, or for one singer with a strong feeling (quite possibly justified) of what key for what song suits her voice best) we have to do it for practical rather than artistic reasons - even perhaps to the key a semitone lower, which can easily literally sound like a "downer". The artistry comes in making the change sound good.

There are many techniques. You can write a series of chords leading ingeniously to the dominant 7th of the new key. You can pivot on a note common to both keys. Very often it's best to just jump, in a completely un-contrived way.

If you want different definitions for "key change" and "modulation", the former describes where you're going, the latter describes your process of getting there. But they're interchangable terms really.

As other answers are demonstrating, whatever key you choose to go to, 'theory' will find a justification for it! Theory Describes, It Does Not Command.