"Briefly," he says "it is a technique by means of which simultaneous combinations of tones, or chords, of a very specific type called triads are arranged in successions to create meaning... the relationship that is established between the chords in succession arouses in a listener the expectation that when one chord is sounded another will follow. If the expected chord does not sound, we are left with a feeling of incomplete meaning, as if someone had said, "The cat sat on the." There exists what we might call a normal cycle of chords, in which a constant cyclic movement takes place, starting from a tonic triad that is the center to which all others relate, proceeding through states of increasing tension to climax and resolution and back to the tonic triad, known as a perfect cadence. We have all been trained from early childhood to recognize this succession and respond to it, and we know what to expect even if we cannot put a name to the successive chords as they are sounded."
Small, Christopher (1998) Musicking