Music is a complicated business but it is furthered complicated by the fact that there are various schools of theory that are used to try to explain it. There are a couple of reasons for that.
The first reason is that the increased understanding over the centuries of how music works has sort of invalidated some of the teaching before it. Look at it this way: a few centuries ago, the medical profession believed that bleeding patients would cure illnesses but we now know better. The same is true in music.
The second reason is just simply that the leaders in different genres of music tend to look at the theory of music very differently. They classify ideas differently. It is not a right or wrong thing. It is just the way it is.
So, I give you that background as a bit of a disclaimer for what I am going to talk about today. When I talk about music theory, I am discussing it from a modern mindset rather than the classically-oriented mindset that many of you may have learned in college. That being said, in general, what I am going to say is pretty widely accepted.
OK, so let’s get to it… Chords are often classified in three different groups: tonic, subdominant and dominant.
Tonic: the place of rest or resolution in the key. The I chord is typically the strongest tonic chord.
Subdominant: a no-man’s land kind of place away from tonic that often moves to dominant. The IV chord is most often associated with subdominant.
Dominant: an unstable place that most often wants to resolve to tonic. The V chord is the most common dominant chord by far.
Typical music (including 99% of the hymns in your hymnal) will follow a very basic rule. Chords move in cycles from tonic to subdominant to dominant back to tonic. There are always exceptions but that is very typical. If you pick up a traditional hymnal, you could look from now through next week and probably would not find a V chord that does not move to tonic.
There is one exception and that is this: subdominant often moves back to tonic rather than to dominant. Most commonly, you see this as a IV – I progression.
Now, here is where things get interesting. There are numerous chords that fall into those three classifications besides I, IV and V. For example, variations of the iii chord and vi chord are also considered tonic along with many other chords. The same is true for subdominant chords and to a lesser extent, dominant chords.
One of the basic rules of reharmonization is that if you recognize the category of a chord, you can substitute other chords within the same category. That means if you have a tonic chord, you can substitute any other tonic chord. There are 15-20 possibilities and the only restriction is just how good it sounds (often because of the relation of that chord to the melody).
I am going to stop here for today but we will address this in more detail over coming weeks. One thing I do want to close with is this. Over time, even while the general classifications of chords have changed, there have been changes in the perception of which chords belong in each classification.
Things will get more practical in coming posts. Stay tuned…