Bach’s music contains several exceptions of conventional theories. An example is the sequence of the entries of Fuga 1 of the WTK1. The usual beginning sequence is subject- answer-subject-answer instead of this, Bach used subject-answer-answer-subject. This exception can be understood looking at the applied construction.next

Also other exceptions like parallel octaves, by example used in Fuga 10 and 19 can be interpreted by structure.next