A chord progression is a sequence of chords with the purpose of establishing a tonality founded on a key, root, or tonic chord.
Chord progressions ...
Chord progressions are abstractly described by Roman numerals, where each number is a degree in the scale.
Upcase Roman numerals are used for major chords, and lowcase for minor chords.
Some common progressions:
The choice of chord alterations in a progression depend on the compatibility of chords for the scale being used.
So the first step is to determine which chords are compatible with the chosen scale.
For the following example, we will use the Major (Ionian) scale.
Mapping each note in the scale to a degree, initially yields:
Building triads for each degree, using only the notes of the scale, gives:
This helps us further refine the previous table, to include the nature of each chord (major/minor/augmented/diminished) .
This produces an initial "palette" of compatible chords to work with this scale.
Next, try to find additional chords matching the scale. Explore possible suspended, quad-chords (6th, 7th), and extended chords (9th, etc).
All of the following chords fit the Major (Ionian) scale in C. [some, not all, possibilities are shown]
Continuing this way, we can produce a more complete chord compatibility chart for the Major (Ionian) scale.
This gives a wider "palette" of chord alterations to choose from.
Which chord alterations to choose, depends on the melody, and on the mood you want to project.
The next step is to produce a chord progression.
There are several approaches to building chord progressions: