Mib: Mib, Ab, Bb, Fa7, Dom, 
Todos esto acordes son de la tonalidad de Mib. En la armadura Bb, Eb, Ab, : Triadas; Eb, Fm , Gm, Ab, Bb, Cm, Dm(b5).. Todos menos F7 que es el quinto grado de la tonalidad de Bb. Fm se convierte en F7, nos trasladamos momentaneamente de la tonalidad de Eb a la tonalidad de Bb, tonalidad cercana pues en la armadura tiene un bemol menos, desaparece Ab y así podemos hacer fa7 : fa,la,do,mib.
Versión en do mayor
[C] I gave a letter to the [Am] postman,
[Dm] he put in his [G7] sack.
[C] Bright and early next [Am] morning,
he [Dm] brought my [G7] letter [C] back.
(t) She wrote upon it.
[F] Return to [G7] sender, [F] address un-[G7] known,
[F] no such [G7] number, [C] no such zone. [C7]
[F] We had a [G7] quarrel, [F] a lovers [G7] spat.
[D7] I write I’m sorry but my letter keeps coming [G7] back.
[C] So then I dropped it in the [Am] mailbox,
[Dm] and sent it Special [G7] D.
[C] Bright and early next [Am] morning,
it [Dm] came right [G7] back to [C] me
(t) She wrote upon it.
[F] Return to [G7] sender, [F] address un-[G7] known,
[F] no such [G7] person, [C] no such zone. [C7]
[F] This time I’m gonna take it myself and put it right in her [C] hand.
And [D7] if it comes back the very next day,
[G7] (t) Then I’ll understand the writing on it.
[F] Return to [G7] sender, [F] address un-[G7] known,
[F] no such [G7] number, [C] no such zone. [F] [C]