A huge share of the world's hits reuse the same four chords. Not laziness — that particular set is very well built.
Search for chord progressions and you get "I-V-vi-IV", "vi-IV-I-V" and so on. Most of those are the same four chords, rotated.
Rotate the same four
C, G, Am and F, changing only where the loop starts. You heard this comparison in chapter one; now it can be described in numerals.
- I-V-vi-IV (C, G, Am, F)
C | G | Am | F
- vi-IV-I-V (Am, F, C, G)
Am | F | C | G
- I-vi-IV-V (C, Am, F, G)
C | Am | F | G
The first is bright and forward-moving; the second starts wistful and lifts; the third has been in use from 1950s pop to the present. All three use identical chords.
A progression that comes round in four or eight bars and can repeat without feeling wrong. Most pop and game music is built this way.
Why this particular four is so strong
- Home (I), tension (V) and opening-out (IV) are all present, so the cycle of jobs completes.
- Including vi (Am) mixes a little ache into the brightness.
- It works from any starting point, so changing the feeling means reordering, not rewriting.
- It stays inside seven notes, so melodies are unlikely to clash.
Generate over I-vi-IV-V. One progression yields completely different melodies every time.
Generate over I-vi-IV-VThe standards are rotations of a handful of chords. Start the same four in a different place and it counts as a different progression.