I was reading how a fugue plays simultaneous voices in different keys (?) I was wondering how they don't clash with each other. Or to put it in another way, what keys can you play together such that they don't clash. For example, I can't play a C major scale with a C# major scale it would clash. So do fugues have rules as to which scales you can play simultaneously?

Edit: I may have been wrong in my assumption. Looks like all voices modulate to a new key. My bad. But it's possible to have a treble clef and a bass clef not sharing same signature / key.

  • 2
    Could you reference where you're reading from, or which fugue(s) specifically? "So do fugues have rules as to which scales you can play simultaneously?" Depends on who's writing the fugue, and when. Bach would say "Yes." Bartok would say "No."
    – LSM07
    Mar 2, 2019 at 20:18
  • @LSM07 en.wikipedia.org/wiki/Fugue#Exposition I understand that it says that the dominant of the tonic is being played. but still I thought that if I play, for example, a C major scale and a G major scale simultaneously they'd clash. I've never seen a situation before where two scales are played simultaneously in modern music.
    – user34288
    Mar 2, 2019 at 20:26
  • 2
    "I've never seen a situation before where two scales are played simultaneously in modern music." -- See polytonality
    – user39614
    Mar 3, 2019 at 0:01
  • There are some notable pieces of music that do include two voices in different keys; this created a cross-relation, if I remember my terminology correctly.
    – user45266
    Mar 3, 2019 at 1:10
  • The conclusion of Bach's fugue BWV 542 certainly sounds like two keys are being played simultaneously, can anyone elucidate?
    – songololo
    Dec 24, 2019 at 23:09

4 Answers 4


The subject of a fugue is first stated alone, then a second voice is added which re-states it at a different pitch (typically a 5th higher). If this 'answer' is literally transposed it's called a 'real' answer. If it's modified to remain in the tonic key it's a 'tonal' answer.

But the initial statement and the answer aren't played simultaneously! To over-simplify, it's just as if a song has a bar of C chord then one of G.

  • 5
    LOOK at some fugues. Source first, then analysis.
    – Laurence
    Mar 2, 2019 at 23:36
  • I didn't know it was in tandem, I thought it was parallel. I'm simply asking a question.
    – user34288
    Mar 2, 2019 at 23:47
  • 3
    You mean in series? Tandem IS parallel. Fine. But LOOK at some fugues to see how it DOES work before complaining that It CAN'T work! This is your old problem of studying the theory rather than the music.
    – Laurence
    Mar 3, 2019 at 0:06
  • 3
    Only when it's a bicycle! Otherwise I think it generally just means 'together'. At best, it's ambiguous. collinsdictionary.com/dictionary/english/in-tandem
    – Laurence
    Mar 3, 2019 at 1:03
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    @LaurencePayne -- apparently tandem can mean one before the other for horses, too, but this is a spatial meaning. Here we are talking about a temporal meaning, i.e., one statement comes before the other in time. I have never heard anyone use "tandem" to mean sequentially in time (as OP is using it), but always to mean together in time (as you are using it). Even for horses and bicyclists, I think that the point is that they are working together, not one after the other.
    – user39614
    Mar 3, 2019 at 2:49

The wikpedia reference given by the OP in a comment says nothing about "playing voices in two keys simultaneously".

But the assertion that

I can't play a C major scale with a C# major scale it would clash

is not true in any case. The following example doesn't "clash," by any reasonable definition of the word. Every interval is (enharmonically, if not notationally) either a major or a minor third.

C major and C# major scales

Theorists have invented "rules" for writing fugues, but their main purpose has been in marking student examinations, not composing music. One well-known rule book is the so-called "fugue d'école" which was written in the 19th century at the Conservatoire in Paris by Cherubini.

However, it's amusing that about three quarters of the fugues in Bach's "Well Tempered Clavier" would have failed the Paris Conservatoire's composition examinations. Of the eight so-called "essentials" in Cherubini's marking scheme, many of Bach's fugues only contain two or three, which is hardly a passing grade!

In fact, a fugue doesn't have to be in a "key" at all. Here is an example of one which is not. Note: the duration is about 60 minutes - somewhat longer than Bach's fugues. Don't be fooled by the slow start - things start to get more exciting after the first 10 minutes or so...

Of course some people (and perhaps the OP) might not consider that fugue by Sorabji to be "music" at all - but not everybody shares that opinion.


Again, it needs consonance and in order to create a fugue, you have to make the different voicings interlace with each other so that they can all state the subject without clashing.


I don't think it makes sense to talk about a piece being in two keys simultaneously. A human hears a piece of music as one experience, not two independent ones that can be superimposed if the listener wants to.

That said, people have written music in two keys at the same time. They call it bitonal music or polytonality. But this is a theoretical device. Many theorists reject this idea as it isn't sensible and has no explanatory power. Why? Because it is very hard perceive it as two different things heard at the same time. Even if they are different instruments in different registers.

But yes, you can take a piece of music, for example a piano piece, and just change the key signature of the bass clef only and play it. But it doesn't make a lot of sense to do it and it will almost certainly sound very bad.

And yes, a C# played in a piece in C major does clash. Just because it can be done and just because you can even make it sound good, that doesn't mean it doesn't clash. Many intervals are dissonant as well, and we use them. We need things that are dissonant and things that clash to make music interesting. Both saying that you are never allowed to play C# in C or saying that nothing is eve dissonant or clashes, because it can be done if you want is misguided. Music theory explains why something sounds a certain way. And playing a C# over a C chord rather than a C certainly clashes. And the theory explains why.

  • The OP is asking specifically about fugues.
    – user9480
    Mar 3, 2019 at 19:53
  • The OP was confused. See the edit. The question was restated ignoring the issue about themes in fugues being stated in different transpositions.
    – Alcathous
    Mar 4, 2019 at 0:41
  • What? You can listen to music as if it's multiple independent experiences that can be superimposed on top of each other. Just listen to a mashup that involves two or more different audio tracks on top of each other (e.g. a mashup of different versions of the same video game character's boss theme) or a karaoke version of a song, then the original song. Occasionally, you run into music that plays an accompaniment track first, then the accompaniment with its melody on top.
    – Dekkadeci
    Jan 11, 2021 at 13:53

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