A chord progression (or harmonic progression) is a series of musical chords, or chord changes that "aims for a definite goal" of establishing (or contradicting) a tonality founded on a key, root or tonic chord and that is based upon a succession of root relationships. Chords and chord theory are generally known as harmony. An analysis of the melodic and harmonic structures of a song is part of ARC Music's next set of lessons -- and one that can reveal what a composer tended toward during a specific period of time.