Von der Null's Moderne Harmonie is an analytical book, therefore different than a Harmonielehre. I will come back to this shift from harmony-exercises to -analysis, and the shift of composers to musicologists/music theorists as writers of these 'theory' books in chapter 2.
Until the mid-19thcentury, conservatoires had been using pedagogical textbooks that dealt with the musical vocabulary of its own time, or at least its recent history. But after that, the textbooks have become victim of the before-mentioned deadlock, which resulted in a standstill that continues until today, making the gap between contemporary music and music theory education bigger every year. Why did this happen? This question has no easy answer, but in the following three chapters I would like to discuss three aspects that relate to this problem:
1. Music theory textbooks were in fact composition textbooks;
2. The increasing complexity of the music and the development into individual compositional styles in the 20th century;
3. The increasing gap between professional and amateur musicians in combination with the decrease of popularity of contemporary music since 1900.
Of course, all three aspects are in close relation with each other, but are worth a separate investigation.
The final 4th chapter of my research is on non-compositional music-theoretical training, which is not finished yet.