The use of each key in Western music?

Question

I've been looking into variations on the following question: why was X piece written in Y key? For instance, why did Beethoven choose to write the Moonlight Sonata in C# minor? Presumably we can transpose a piece and, in theory anyway, it will still be the same. I know that this question has been asked before, but I'd like to expand on the previous questions asked by other posters. In particular: There are a number of opinions of composers about each key. C major is considered "innocent and childlike", for example, but one source refers to F-sharp minor as "A gloomy key: it tugs at passion as a dog biting a dress. Resentment and discontent are its language.". I disagree with that opinion on F-sharp minor (I find it to be a playful key in which dances "make sense"). So I suppose the question really is: how does a composer develop their particular style and thereby attribute certain desirable qualities to each key? For example, I've already chosen F-sharp minor to be a playful, dance-like key and G-sharp minor to be a slow, haunting key. That's my personal opinion, but I can't define why I hold it.

Answer 1

Some people have perfect pitch and so each key is truly different to them, even on a piano or in equal tempered tuning systems. They develop their own individual associations with each key.

But for most people, it's often a question of what key is most practical on the instrument you're writing for. Pianos are often very friendly to keys with five or six flats, for example, so there is a lot of piano music by composers like Liszt written in five or six flats. The idea is that it lands on a lot of black keys which are easier to press accurately than white keys in virtuoso passagework since they stick up from the keyboard. String instruments are very friendly to keys between two flats and three sharps because it allows us to hit lots of open strings, adding resonance and again making lots of complex passagework simpler.

Sometimes it's a question of what is easier to read: more flats and more sharps make music more difficult to read for most players, especially below professional level. You will almost never see piano music for beginners written in five flats, even if Liszt did it a lot.

Sometimes it's also just a question of historical association. If a critical mass of composers before you picked D Major for triumphant brassy marches, it becomes "the triumphant march key" in many people's heads, and so even more marches get written in D Major, reinforcing the association. There's no reason it could not have theoretically been some other key, but it just worked out that way because of historical inertia. And whether you have perfect pitch or not, you might be heavily influenced by this.

Answer 2

I don't think you have to define why you hold a certain opinion on what a key emotes to you. A part of the process of composition is being able to simply make those connections for yourself and the fact that you are doing that is indication (to me anyway) that you are on a good road. For me, E Major is often very bright (sunrise) while Eb Major is dark (midnight). Others might view it differently and that's ok. Our experience, thought, and musical background all shape how we compose music and to a great extent how we perceive music. As we grow and learn more about different kinds of music, some of our initial thoughts are solidified while others are drastically altered. It is all apart of a continuous process of growth we have as musicians. I hope that was somewhat helpful!