If consonance were the whole story, the most pleasant music would be the most consonant — and it would bore you instantly. It doesn't, because harmony's real currency is expectation. Cheung and colleagues (Current Biology, 2019) modeled 80,000 chords from hundreds of pop songs, quantifying each chord's uncertainty (how predictable the moment before it was) and surprise (how much it violated that prediction). Pleasure tracked the interaction: listeners liked chords that were low-uncertainty but surprising, or high-uncertainty but unsurprising — and fMRI showed the amygdala, hippocampus, and auditory cortex responding to exactly that interplay. In plain terms: set up a strong expectation, then break it (the deceptive cadence, the borrowed chord) — or wander in fog, then resolve simply (the ii–V finally landing). Every device on this site is a machine for staging that gap. Tension and release isn't a metaphor; it's prediction error, measured.