I'm hoping someone can help me with something I don't understand in the intro to Bert Ligon's book "Connecting Chords with Linear Harmony".
In the key of C, A7 would be the secondary dominant of D minor (ii in the key of C). He says the "necessary accidentals" for this are "B flat and C#". I can understand including C#, because it is is the 3rd of A7. However, why B flat?
If it helps, here is the context for this information:
New key area to be tonicized
ii = D minor
Secondary Dominant
A7 (V7/ii)
Necessary Accidentals
B flat and C#
thanks in advance,
Tom