Introduction to Chord Progressions and Function

A Chord Progression is a series of diatonic chords within a certain key, that can be labeled using roman numeral and figured bass notation. Within chord progressions, each chord has a Function indicating the expected chords to precede and follow it, hence delineating its role in the progression. The primary chords have the following functions:

The tonic triad is a resting point in the progression, and can serve as a restart to it. Any chord can follow a tonic chord.

The dominant triad or seventh chord generally leads to the tonic, unless a progression is deceptive, in which case the submediant triad follows.

The subdominant triad almost always leads to the dominant triad, but can also occasionally lead to other triads, and often leads to the tonic in a plagal motion.

Notice that deceptive and plagal progressions are not cadences - even if they use the same two chords, they may or may not occur at the end of a phrase. Deceptive or plagal cadences are a type of deceptive or plagal progressions.

The below chord progression, I-IV-I-V7-I in G Major, shows some of these basic functions of these chords. When writing chord progressions, common tone spellings are usually attempted to create smooth voice leading. The chords may also be inverted, in which case figured bass notation would be employed as well, but are not here.