Diatonic can be defined as: of or using only the seven tones of a standard scale without chromatic alterations (The Free Dictionary by Farlex). Therefore, diatonic chord progressions contain chords build on only the seven pitches within a given key signature. A triad or seventh chord can be built using each pitch of a major or minor scale as a root for the chord. These chords are given roman numeral labels that correspond to the scale degree within the key that is the root of the chord. In major keys, the diatonic triads and seventh chords are simply constructed by utilizing the root, third, fifth and seventh (in the case of seventh chords) of each scale degree while remaining within the given key signature. A list of the diatonic triads and seventh chords in the key of C major is provided below.
The restrictive nature of diatonic key signatures cause the triads and seventh chords of diatonic progressions to have set qualities. For example, the one chord of any major key will always be a major triad or seventh chord. The six chord in a major key will always be a minor triad or seventh chord. A summary of all of these qualities is found in the chart below.
Within the larger scheme of harmonic movement, all songs end on the tonic harmony. This final cadence is usually achieved by a dominant chord that resolves to the tonic. The dominant chord is usually approached by either a two or four chord. Subdominant or supertonic harmony can be approached either directly from the tonic, or by the use of the seven, three or six chords. This type of large scale harmonic motion corresponds to the names given to each diatonic chord (as listed in the previous paragraph). An outline of this large scale harmonic typical harmonic motion is provided below.
In addition to diatonic chord progressions, chromatic progressions are also used in music. There are several common methods for utilizing chromatic chord progressions. Mixture is a method in which chords from the parallel minor diatonic sequence are used within a major diatonic progression. Circle of 5th (two-five-one) progressions can be used to created temporary alternate key centers. In this type of situation, a chord you are traveling to (like a four chord) could be temporarily perceived as a one chord, and a two-five-one progression can be used to travel to this chord. Chromatic leading chords can also be used to travel to diatonic chords. The most popular chromatic leading chord is the diminished seventh chord that is a half step below the chord you are traveling to. Seventh chords with altered upper extensions can be used to introduce chromatic pitches. Finally, tritone substitution can be used to created altered two-five-one progressions. Every dominant seventh chord shares a tritone shell (3rd and 7th) with another dominant seventh chord a tritone away. These two dominant seventh chords can be used interchangeably in two-five-one progressions.
The best way to acquaint yourself with common chord progressions is to listen to the progressions used in the music on your playlists. Listen first to the bass line and use it to determine the roots of the chords. Then listen for the upper tones to establish the quality of the chords. In addition, experiment on either a guitar or piano forming various chord progressions. Listen to the character of each progression and the relationships between the different chords. Expand your knowledge by developing strategies for connecting progressions. The study of chord progressions can be an advanced musical topic, but an understanding of this topic will unlock the knowledge needed for even larger future topics.
This Learning Music With Ray video discusses chord progressions. It is a study in the typical harmonic patterns used when traveling from one chord to the next in a sequence. In this video, I discuss both diatonic and chromatic chord progressions. I provide a detailed illustration of the diatonic triads and seventh chords found in both major and minor keys. I discuss the large scale harmonic motion that is found in most pieces of music. Finally, I provide examples of common diatonic and chromatic chord progressions (including ii-V-I progressions, mixture, altered chords, chromatic leading chords and tritone substitution).