Composer Suzannah Doyle shows how to change a song from one key to a new one by substituting chords from one chord family (in a specific key) with ones from a different family of chords (This video covers chords in a MAJOR key, where the 1, 4 and 5 chords are major). Every key has 7 chords, so by thinking in chord NUMBERS, you can easily change from one set of chords (in a key) to those from a different key. Transposing can make a song easier to sing, and easier to play on some instruments (e.g.