The ii-V-I and Other Common Progressions

ii-V-I is the T-PD-D shape from the last lesson in its single most common form — so common in jazz standards, pop choruses, and classical cadences alike that it's usually just called "two-five-one." The predominant ii sets up the dominant V, which resolves to the tonic I; each root moves down a fifth (or up a fourth) into the next, which is itself one of the strongest bass motions in tonal music.

That falling-fifth motion is worth isolating on its own: vi-ii-V-I extends the same logic one step further back, and the circle-of-fifths progression (moving root by root in descending fifths, e.g. iii-vi-ii-V-I) is a workhorse for both classical sequences and jazz turnarounds.

I-V-vi-IV (and its rotations, like vi-IV-I-V) is the loop behind an enormous share of pop and rock songs — it works as a loop precisely because none of its four chords is a strong final cadence on its own, so it can repeat indefinitely without feeling finished until the songwriter chooses to land somewhere else.

I-vi-IV-V (sometimes called the "50s progression") swaps the order and adds a real V-I motion at the loop point, giving it a slightly more resolved, doo-wop-era feel compared to I-V-vi-IV's more open, contemporary one. Learning to recognize these shapes by ear is often faster than reading them — try picking one out on the piano the next time you hear it in a song.