music theory question - use of flats/sharps

I noticed over at http://www.ezfolk.com/uke/chords/ that they label their A# chords as Bb, and follows a flip flop pattern through the rest of the sharps and flats. I know they're the same note, but I'm just wondering if there's some kind of rule or theory behind this.

If I'm just looking at the Bb chord in a book, would it be incorrect to label that as an A#, or does it bounce back and forth? Similar to C#/Db, Eb/D#, etc.

I know when constructing certain scales like major scales, you can only use 1 of each letter when writing the scale down. So in the F major scale for example ( F - G - A - Bb - C - D - E - F) you wouldn't be allowed in written form to write out that Bb as an A#. I'm really just curious as to whether or not there's a rule to labeling such notes *outside* of scales. Sorry for the weird question

My take:

Musicians will understand enharmonics (the in between notes that you are curious about) most any way you write them, but some ways might be "incorrect" - Mozart would have a fit. Most of the time if I'm writing out enharmonics for something not related to a key, I use both labels with a slash in between (C#/Db). Like when I'm tabbing out scales I'll go: C scale, C#/Db scale, D scale, etc... Sometimes though if I'm talking to somebody or writing something out for my own use I use a flip flop method. C#, Eb, F#, Ab, Bb. As opposed to Db, D#, Gb, G#, A# which sound kind of funny to me. But usually you will have some sort of context to relate to. Then you would use the proper "key labels" - D# in the key of E, Eb in the key of Eb, etc...

If I'm just looking at the Bb chord in a book, would it be incorrect to label that as an A#, or does it bounce back and forth? Similar to C#/Db, Eb/D#, etc.

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Nope, it wouldn't be wrong, but when you can, use whatever is related to the key.

Usually, the less flats/ sharps around the better, when it comes to chord writing. In the key of Bb, there are only three flats, where as in the key of A#, there would be so many sharps, that you would start having double sharps. Usually the keys that are used enharmonically are: Gb/F# B/Cb and Db/C#. Otherwise it is easier to write chords in their simpler form.

Also, (I know this is true about writing music, but not too sure about chord writing) when writing something that will have a leading tendency, it is better to write B -> A# -> B, because this gives more of a "leaning" feeling to the second Bb. More so than B -> Bb ->B.

Hope this helps.

STEM said:

I know when constructing certain scales like major scales, you can only use 1 of each letter when writing the scale down. So in the F major scale for example ( F - G - A - Bb - C - D - E - F) you wouldn't be allowed in written form to write out that Bb as an A#. I'm really just curious as to whether or not there's a rule to labeling such notes *outside* of scales. Sorry for the weird question

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Chords are not outside of scales. They are buit from scales. You name the chord after the note from the scale from which it is built. You find the scale from the key of the song*. If you are in the key of F then a IV chord should be named Bb rather than A#. You might see A#m7b5 as a chord VII if you are in the key of B for example. It gets tricky if the chord isn't in the scale belonging to the key of the song. That usually means that the key has changed (modulated) to another key temporarily.

*or you find the key of the song from the scale it is buit from. It gets a bit circular.

Dibblet said:

Chords are not outside of scales. They are buit from scales. You name the chord after the note from the scale from which it is built. You find the scale from the key of the song*. If you are in the key of F then a IV chord should be named Bb rather than A#. You might see A#m7b5 as a chord VII if you are in the key of B for example. It gets tricky if the chord isn't in the scale belonging to the key of the song. That usually means that the key has changed (modulated) to another key temporarily.

*or you find the key of the song from the scale it is buit from. It gets a bit circular.

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Right. It has to do with key signatures: The notes that are "normally" sharp or flat in any given key. In the F major scale, the B note is flat. Therefore the Bb/A# chord occuring in the key of F major would be called Bb, not A#.

If you were a masochist and decided that you wanted to call it E# major instead of F major, then yes, that same chord would be justifiably called A#. You would also call the C chord a "B sharp", and you'd have to call the Gm chord an "F double-sharp minor", for example. As you can see, it's much easier to call it F major and only have to deal with the one flat!

JJ