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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?

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    Not sure that I entirely agree with the premise. You may be correct but how thoroughly have you checked? A quick look shows me that Haydn Symphony no. 12 is in E major, so that makes two. Also not all movements of a symphony are in the same key (although the first and last often are) - have you checked the keys of the second and third movements of these works?
    – JimM
    Commented Dec 29, 2022 at 15:37
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    Looking through Haydn's keyboard works we find many more. This category in IMSLP, not exhaustive since it's only the 42 works tagged as "harpsichord," has two A-flat majors. Also, beware of the "evolutionary fallacy": if it can be confirmed that these were rarer in the Classical period than Romantic, I'm not sure that it follow that they were also rare in the Baroque; Bach has a lot of movements with lots of flats, even outside of the Well-Tempered Clavier. Commented Dec 29, 2022 at 16:47
  • @JimM 2 out of 104 is still less than 2 percent, my point stands. Also, modulations in the classical period are often limited to the dominant or the subdominant, with very brief "modulations" in development sections. Even movement keys often stay in the 3 sharp/flat range.
    – OprenStein
    Commented Dec 30, 2022 at 3:43
  • Hot take: it's because keys with excessive sharps/flats are confusing and bad.
    – geometrian
    Commented Jan 1, 2023 at 9:32

5 Answers 5

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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.

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    Expanding on the impact of temperament, meantone temperaments included a wolf interval, usually the fifth between G♯ and E♭ which rather sharp and perceived to be distinct from the other perfect fifths in the tuning. Also worth noting on the subject: This is remedied in equal temperament by making everything out of tune by the same (generally recognized as acceptable) amount.
    – Theodore
    Commented Dec 29, 2022 at 18:54
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    By "recirculant", do you mean well-tempered? Equal tempered? Something else? Commented Jan 1, 2023 at 4:39
  • As I understand the term, recirculant means that all keys are playable but not identically tuned. Werkmeister III or Kirnberger III or some of Wendy Carlos' stuff would be examples.
    – ttw
    Commented Jan 1, 2023 at 14:01
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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.

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    One reason to write in A flat major would be that key signatures with lots of black keys are easier for pianists. Beethoven wrote a lot for piano.
    – ojs
    Commented Dec 29, 2022 at 17:09
  • His academic exercise produced some of my favorites! The F minor one in particular.
    – Stian
    Commented Dec 29, 2022 at 22:23
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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.

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  • Just gotta say: Horns used to have attachable pieces of tubing we call crooks which allows to change the tuning of the instrument. If you have the chance to attend a performance with old instruments you might spot the horn players having multiple crooks dangling from their notestands.
    – Lazy
    Commented Dec 29, 2022 at 20:04
  • Yes, I know about crooks. But does that mitigate the other instrumental issues? Commented Dec 29, 2022 at 21:23
  • I changed that paragraph to be more general, rather than getting into horn crooks. Commented Dec 29, 2022 at 21:30
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    No, but I just wanted to point out that the horn is not a particularly suitable example. For a different example many old woodwinds have many chromatic notes that are awkward to play or not even possible to play at all, making playing certain keys very challenging on let’s say a baroque style bassoon. Also on strings you’d usually try to avoid keys that do not allow for empty strings.
    – Lazy
    Commented Dec 29, 2022 at 21:49
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    Yes, that's understood. I reworded to make this particular point more general. The OP just needs enough to get them pointed toward reading up on orchestration and the history of instrument design. Commented Dec 29, 2022 at 22:12
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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.

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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.

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