When it comes to chord progressions, something that is good to keep in mind is the idea of stable chords and instable chords and how to use them.
Stable chords are the chords I, IV, and V regardless of minor or major key. These chords are considered stable because they stablize the tonal key of the music.
All other chords, II, III, VI, and VII are instable chords. When they are played they change the tonal key of the music, even if it's temporary.
What I mean by tonal key can be illustrated by looking at the chord and what chord it makes up within the key. Take C major, I, IV, and V are all major chords. They stablize the tonal key of the music, major. Now look at the instable chord in regards to C major, they are all minor, except VII which is diminished.
When we look at the two types in music. Stable chords are used more often, especially in rock and folk music. ex. (c major) C-F-G (I IV V). How many times have you seen that progression, or one similar? Why? Because these chords have the strongest sense of key, and any simple melody can be harmonized using just these three chords. Try it, Take the first progression Ace wrote, record it. Then solo or sing over it, you can probably come up with a million melodies and they all work.
You can also come up with any sequence using those three chords, and then read the next part to see how to manipulate them.
When it comes to fitting the instable chords into the progression, they are usually only thrown in a few times to mix things up, or as a substitution, or as a transisition to get somewhere else. I'll give an example of each.
Mix things up. Instead of playing I IV V, you could go I VI IV V. A very common chord progression. I IV II V, or anything you could come up with.
Substitution. Each stable chord, in the case of the major key has a minor substitute. These are found by moving up or down a third. Example C major's minor subsititute is A minor. I don't think I need to explain. Also E minor. The others are: IV is II and VI; and V is III and VII.
Certain ones are more common than others, so I'll point that out. A minor is a more common sub for C major, than E major. II is a more common sub for IV, than VI. III is more common than VII, because VII is hardly used. But whenever it is thought to be used, V is subbed instead of VII. You rarely find the VII in music. The exception is in a minor key, VII is quite common. I VII VI V.
Here's an example of a progression with a substitution. II V I instead of IV V I.
Transistion. Using the unstable chords can change the tonal key from major to minor or minor to major. If you understand modes than you should know the sixth note (VI) in the major scale is where the minor mode starts. Take the instable chords within C major and translate them to the minor mode. Suddenly VI becomes I, II = IV, and III = V. Suddenly you have the stable chords for a minor tonal key. So you can start off in a major tonal key with: I IV V VI II III. The first three chords carry a major tonal key, while the the last three carry a minor tonal key. So if your writting a tune that has a major sound and you want to bring in a part where is sounds minor, that's how. Even vice versa, minor to major.
The most common movement from chord to chord is in fifths. I to V, VI to II, and so on. Movements by seconds are the strongest, V to VI, III to IV, and so on. Have fun! :D
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