I'm studying 16th century counterpoint.
My book says, when writing a melody for second species, augmented 4th or augmented 5th shouldn't occur between strong beat and a strong beat.
But this is not between the strong beats isn't it ? It's past the strong beats so I assume it's fine but why is it saying this is a bad example ?
The issue here is that the consecutive scale fragment spans a augmented 4th. It forms what is called a compound tritone, and many counterpoint textbooks advise against it, as in the section below, of Schoenberg's Preliminary Exercises in Counterpoint, p. 6:
In other words, even if the interval of a tritone is 'filled' with the notes between the 4th and the 7th, it is still to be avoided. In your example, if the note following the F were and E, there would be no problem, as the interval between the ends of the scale fragment would have been a perfect fifth.
