Bbsus4 is Bb, Eb and F — with the third replaced by the fourth.
It sounds suspended mid-air. Played before the plain chord it is the oldest tension-and-release move there is.
Suspended — classically it resolves down onto the third.
Also written Bbsus or Bb suspended 4th.
Bbsus4 holds the tonic over into the V, where the third should be, then lets it fall a step to the third. The V is the chord most often treated this way, and more often still the fourth is left hanging and never falls.
Listen for: The tonic holds into the V as its fourth, falls a half step to the third, and rises back home.
Heard in“Sunny”“In My Room”“California Dreamin’” (left hanging)
The 4–3 suspension isn’t only for the V. Bbsus4 can fall to Bb as the IV of F major, and a minor tonic can be suspended the same way.
Heard in “Honky Tonk Women” (IV), “Love Is Blue” (i)
In which keys. Every note of Bbsus4 belongs to C minor, C# major, Eb major, Eb minor, F minor, F# major, G minor, Ab major, Bb major and Bb minor.
Every note of Bbsus4 is in Bb minor pentatonic, Bb blues, Bb major, Bb natural minor and Bb dorian.
Each of those is a page: the scale across the neck, and the chords it harmonises into — which is where Bbsus4 sits in it. Every scale.
Change one note of Bbsus4 and you have (the fourth becomes the major third), (the fourth becomes the minor third), (the fourth becomes the second), (add the second), (drop the fourth) or (add the flat seventh).
Bbsus4 is a suspended chord — root and fifth, with a second or fourth where the third would be — or nothing at all. Suspended and power chords on every root.
The common shapes and the derived voicings come from different places, and both are explained in how this site is built.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.