I was looking at Cold Duck Time :

enter image description here

Where the key signature is F major. On the second bar, the bass line says that the A is to be played natural. The key signature doesn't have Ab, but the chord (Bb7) that is being played at that bar has; does this chord imply that if it weren't for the natural sign, the A was to be flat?

How am I supposed to play the A at the 4th bar? Natural or Flat?

  • The chord does imply Ab, which is part of Bb7. Bars either side contain Eb, part of F7. Can't see why the first A is actually marked natural anyway!
    – Tim
    Jan 28, 2016 at 11:50
  • 1
    In general, regardless of your example, no one chord by itself implies a change in key. It requires a progression of chords creating a cadence to create a change in key. In general, jazz involves frequent very brief excursions into chords that are outside the given key or that contain notes outside the given key, but these are so frequent and brief that they do not necessarily constitute a key change. Furthermore most jazz lead sheets are notated with a single key signature even though the piece clearly moves into one or more different keys at certain points.
    – user1044
    Jan 28, 2016 at 13:15
  • In one style of jazz lead sheet writing, no key signature is used at all even though the melody line and the chord progressions clearly indicate one or more different keys. In this style of lead sheet notation, lots of accidentals are put in front of notes as needed, rather than having the accidentals notated in a key signature.
    – user1044
    Jan 28, 2016 at 13:19
  • Kinda funny song title. "Cold Duck" refers to a brand of cheap sparkling wine (faux champagne) made in Canada that was popular in the 1960s and 1970s.
    – user1044
    Jan 28, 2016 at 13:22

2 Answers 2


No a chord does not come with its own key change. What it does come with is its own set of notes that will define the chord regardless of what key you are in. A Bb7 will always be spelled Bb-D-F-Ab. Assuming those naturals are suppose to be there they could be curtosy accidentals there to remind you the A is natural even though the overall harmony at that point is a Bb7. I know if I was just given the chord progression I would only use an A as an aproch or passing tone.

I however think it's a printing mistake as another version I found with a very similar bass line, but with flats instead of naturals.

enter image description here


Tried listening to several recordings, and the only one I caught actually went to Gb/F# instead of A ! Making the chord closer to Bb7 aug 5. Might be worth while doing the same.

Answering your lead question - a chord does not imply a change of key sig. In this case, if it did, there would need to be an Eb as well in the key sig. to get to Ab, thus stating 3 flats - Eb. As it is, the piece sounds like it could be in 2 flats, with the F7 pushing towards a Bb. Maybe F Mixolydian?

Checked on #Jazz Clefs# and the note is written as Ab there...

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