Why does music from the Classical era rarely use keys beyond 3 sharps/flats?

Question

This is just something I noticed when looking through music from this period. They almost never go beyond 3 sharps or flats. For example, Mozart's symphonies: https://en.wikipedia.org/wiki/List_of_symphonies_by_Wolfgang_Amadeus_Mozart

Mozart's string quartets: https://en.wikipedia.org/wiki/List_of_string_quartets_by_Wolfgang_Amadeus_Mozart

Or Haydn's 104 symphonies, of which only one goes beyond 3 sharps(No 29 in E major) https://en.wikipedia.org/wiki/List_of_symphonies_by_Joseph_Haydn

This is a recurring pattern. You can almost never find a piece of music from this period in Ab major, or in C# minor. I had to look pretty hard to find an exception. Why did composers from the classical period stick to 3 sharps or flats, and never go further? Also, why was it Beethoven who seemed to break this tradition, writing more frequently in keys with more accidentals?

Answer 1

The primary reason was the widespread use of some type of meantone tuning. Unlike the currently popular equal temperament, different keys had chords that are somewhat out of tune. There were recirculant tunings that did allow all 24 keys to work well, they were not always used.

Another reason was the lack of keys on brass instruments; on all brass instruments (except trombones or sackbuts), one only had access to the overtones of the instrument supplemented by inserting the hand into the bell of the instrument or by varying wind pressure using the lips. An instrument was really only useful in its own key and maybe some nearby keys. There were "crooks" that could be inserted into the instrument to change the length of the tube. Woodwinds also had fewer keys before the Bohm system of keys.

On the other hand, pieces may modulate quite far in Baroque and Classical pieces.

Answer 2

First, I would turn the question around: why would music from the classical era use such keys?

That's IMO still a question to ask oneself: why use a key like A♭ major, when putting it in G major or A major would give almost the same registers?

Of course, nowadays with guitars and (MIDI-) keyboards being the most common instruments, musicians tend to think of all the 12-edo keys as being more or less equivalent, but this was very much not the case historically. The first music that shares our western note names didn't have sharps-and-flats at all. The first accidental that got used was the “round b” that begot the ♭ symbol, and it was only applied to the note B, i.e. B vs B♭ (called H vs B in many languages). The distinction being essentially in where the tritone appears. It was not a matter of just filling in the gap between A and B.

As time went on, more accidentals were added, but they were still constructed via diatonic scales, not from a “the octave is divided in 12 steps” perspective. And they actually had significant tuning problems, until the first well-tempered tunings arrived. Whereupon, sure enough, Bach made it a personal endeavour to write music for all those weird keys that had become available, but it was at that point more an academic exercise than a practical thing for musical performance.

For Mozart and Haydn, keys with more than 3 sharps/flats would have still been fairly exotic curiosities. Many of the instruments of the era would have had a hard time playing them, and even for the instruments that are in principle capable of it quite well, the players would have struggled. In fact, even today keys with many sharps or flats put some extra mental and/or physical burden on players. Nevertheless, neither of them were afraid to put in a liberal dose of accidentals to achieve exciting modulations.

As to why Beethoven used those keys more often? Well, he was generally a progressive mind, always eager to explore new paths, even if they were rough. If he saw some value in doing something differently, he was more likely to actually do it than Haydn and Mozart were.

Answer 3

In part it's about the history of tuning systems. Look up temperament and J.S. Bach's Well Tempered Clavier to get the basic story about tuning systems and their implications for playing in all keys/all keys being equally usable.

Also, it is about the tuning of instruments. When you have things like winds designed around specific pitches, open strings tuned to specific pitches, keyboards tuned to specific pitches, you tend to stay within the confines of those fixed tunings. Those tunings tend to center around C, G, D, F, Bb. Look up the Boehm system for some of the important history of wind instrument development.

Finally, don't get too fixated on the key of music stated in the title. Keys change through the progress of a classical works. Probably the key change that is most likely to introduce more sharps/flats than three is a change between the parallel major/minor. You can find examples in the minuet and trio sections of Haydn piano sonatas. Those have examples of parallel key changes like Bb to Bb minor (5 flats), Eb/Eb minor, B major/B minor, and C# minor/C# major.

Remote keys are definitely less frequent in the classical era, but they could be used. When tuning systems and instrument design made those remote keys more easily accessible composers explored the possibilities. In part those changes lead to the stylistic changes of the Romantic era.

Answer 4

To amplify Lazy's comment, baroque and classical period woodwinds were in most cases required to use fork fingerings to play sharps and flats. On baroque bassoon, for example, the fingering for c sharp would be the first two fingers of the left hand and the first finger of the right hand. So the far-flung keys were not really practical although you can find occasional examples of them.

Answer 5

What I've observed was music gradually turned from more sharps to more flats over time and I personally see the development of the valve for brass instruments in the first half of 19th century as the turning point. Strings sound fuller in one of the keys of the open strings (C, G, D, A, E) and those would be the keys the classical period favors, in addition to keys that favor woodwind and brass with no valves (F and Bb). Bach wrote in all 24 possible keys for the keyboard, of course, but even keyboard instruments were affected by this as it was undergoing changes in its role from basso continuo accompaniment to a powerful solo instrument (the modern piano). So I would attribute what you've observed to the technology available back then. Mozart did not have the instruments we take for granted today.