I'm confused as to how I should play the second note below, B#. Does it mean it's C? It is possible? In which case, why is it written like this, and not just C?

enter image description here

Sonata quasi una Fantasia, First movement (Moonlight Sonata, Beethoven, OP.27 No 2) -- https://www.8notes.com/scores/1754.asp

  • 5
    Although there is no context given for this tiny snippet, it looks like this is in C# minor and the harmony is a G#7 chord, which is the dominant in that key. We always spell any type of G triad with the letters GBD.
    – user9480
    Commented Feb 7, 2015 at 5:04
  • It needs actually a C with a natural sign on it. C# is in the key.
    – Vighnesh
    Commented Jul 22, 2023 at 6:26

13 Answers 13


In a key where there are already some sharps (or flats) in the key sig., as here, every time one of those notes is played, it has to be sharp (or flat). In E, or C#m, the key here, every other note is natural - E, A, and B. So if a note sounding like a C needs to be played, it can't just be written as a C, because the player would automatically sharpen it, to play C#.

So there are two ways to write this actual note: C natural or B sharp. It will depend on the technical nature of things, like what would that note have been before it needed to change. If, for example, the harmony underneath produced an augmented chord, where E, G#, B became E, G# B# that would be how it was written. If, on another tack, the chords underneath went from A maj. to Amin., then the changed note would not be C# any more, but C natural.Thus spelling the chord properly, even though it's only one note out of that chord.

On the face of it, it seems unnecessary, but from a technical point of view, it is correct. Lots of players would probably be just as happy reading a C natural, but the next glitch MAY be that any subsequent C# in the bar would then have to have an accidental written in, which is extra stuff to read.

  • 18
    also, FWIW, in some tunings/temperaments/on some instruments, C is actually slightly different from B# etc, see en.wikipedia.org/wiki/Sharp_%28music%29 & en.wikipedia.org/wiki/Flat_%28music%29
    – user10132
    Commented Feb 4, 2015 at 18:23
  • 2
    "the next glitch MAY be": in fact, the next glitch probably is, because the B sharp is the leading tone of the dominant chord, which is almost always followed by the tonic chord, the root of which is a half step higher than the leading tone. The next most likely chord is the submediant, the third or which is a half step higher than the leading tone. It is in fact extremely unlikely for there not to be a C sharp following closely after this B sharp.
    – phoog
    Commented Jan 24, 2021 at 17:20
  • 2
    @phoog I don't know, I've seen plenty of examples where B goes up to C natural in C# minor, like in the melody of the first movement of Beethoven's Moonlight Sonata. In fact I only really see B sharp in the accompaniment in the first movement of that sonata, the melody uses C natural instead for the same note, at least in all the editions I've seen.
    – Caters
    Commented May 6, 2021 at 19:27
  • 2
    @Caters but this answer is about where the third of the dominant chord goes (whether it was preceded by a B natural or not). The C naturals in the melody are not thirds of the dominant chord but rather the melodic upper neighbor of B natural (V/iii), or, harmonically, ♭VI/iii over a B natural pedal.
    – phoog
    Commented May 7, 2021 at 13:50
  • 2
    Compared with C natural it is a lot easier to read the way it is written as a B♯, because you can directly read it as a major third from the note below. If it was written as a C natural it would be annoying at least for me. Commented Jan 10, 2023 at 19:55

The note is the same key as C.

It is written as B# instead of "C natural" to indicate note's "role" according to rules of classical (musical) harmony.

My guess is this portion of musical piece is written in Cis-moll, and the arrpegio being played is dominant chord (G# B# D# F#). Because in minor tonalities Dominant chord always has VIIth tone (B is VIIth tone in Cis-moll) raised by halftone (so it sounds like dominant chord), you get B# instead of C natural.

This thing is kinda a big deal in classical music and music in era of romantic music (Franz Liszt, Franz Schubert, etc... not sure if Liszt is ) because the same chord can be perceived differently (when played in chord sequence) depending on tonality of the sequence/part where it is played.

Unless you're speaking of atonal music, you can't normally just set sharps/flats/naturals randomly. Hence the B# instead of C natural.

That's the gist of it.

  • 4
    The note is the same key as C. Notes and keys are different things. This thing is kinda a big deal in classical music and music in era of romantic music Nothing here is specific to romantic music.
    – user9480
    Commented Feb 7, 2015 at 4:59
  • 1
    @BenCrowell "Notes and keys are different things." That's nitpicking. We aren't talking about math or programming here. "Nothing here is specific to romantic" You missed "classical". B# instead of C indicates this is dominant chord in minor tonality according to rules of traditional harmony.
    – SigTerm
    Commented Feb 7, 2015 at 17:05
  • 4
    @BenCrowell - you'll find it's the same piano key, that white one to the left of the two black ones...
    – Tim
    Commented Feb 26, 2015 at 19:39
  • 3
    In an English answer Cis-moll should read c sharp minor.
    – guidot
    Commented Oct 24, 2017 at 10:25
  • 1
    The B♯ is much easier to read than C♮, because you can see right away that it is a major third above the G♯. When I play something like this on the piano I read it as a arpeggiated G♯7 chord. That would be disturbed if the B♯ was written as a C♮. Thus a C♮ would slow down the reading process a little bit. Commented Jan 10, 2023 at 20:03

Add disclaimer Some people apparently couldn't understand what I was getting at with this answer, or don't understand humour or whatever, and therefore flagged the answer. I assure you that any misspellings found here are entirely enharmonic in nature, and thus don't matter. Or do they? If you think so, you've got the point I'm making.

It is knot a C. True – if ewe whir asked two play that note on piano (ore indeed most other western instruments), you'd use thee same key/fingering as ewe wood four C♮, butt its still knot thee same note: conceptually. Think off it like to words witch happen two bee pronounced thee same way, butt mien completely different things, are written differently, end even when spoken can bee distinguished, buy thee context.

(End, they are knot really spoken inn exactly thee same way; pronunciation always varies a little. That's also true four music; good singers ore players off e.g. string instruments use knot exactly thee 12edo pitches a piano wood produce, butt adjust there intonation two best match thee context. Normally, thee result is something between 5-limit just intonation end Pythagorean tuning.)

How that works is discussed inn other questions on this sight end elsewhere. Inn this particular case, B♯ occurs quiet naturally as thee third off thee dominant G♯7, leading up two thee C♯ tonic. OTOH, a C wood appear weird end out off context, sins it actually effects thee tonic itself with an accidental. Sow even four an experienced pianist, though heed physically execute thee same movement, C wood bee thee wrong instruction at that point, like it wood bee confusing four a newsreader if he had two reed out thee text off this answer.

  • 6
    Could you tone down the misspellings here? I see what you're trying to do, and based on the voting, so do several other people, but we got some complaints as well. Not sure if the complainants thought you were trolling or just didn't get the intent or what, but it is sort of hard to read, and I think your point is made after a few instances.
    – Pops
    Commented Feb 6, 2015 at 22:14
  • 2
    Your enharmonic spellings are delightfully disorienting
    – user39614
    Commented Feb 1, 2018 at 17:40

Yes a B# is just a C, but it is written that way because that note is function like a "B" instead of a "C". If you look at the notes you have G#, B#, and F#. Look familiar? It's a G# dominant 7th (5th is omitted, but thats not unheard of).

A more focused question on this idea can be seen in this question as to why notes get alternative names.

  • 1
    No, not really, because, as several commenters indicate, this B# is not just a C.
    – Rosie F
    Commented May 3, 2019 at 8:28
  • 2
    @RosieF B# maps to C on a piano. On other instruments that's not always true, but again we are just talking about piano. This answer states it's spelled that way for functional reasons which several other answers Also do.
    – Dom
    Commented May 3, 2019 at 11:58
  • @Dom is there any instrument where there are separate ways to play B sharp and C? In my experience alternate fingerings are usually discussed in terms of which one is higher or lower, not which one belongs to which enharmonic spelling of a note. Besides, whether B sharp should be lower or higher than C depends on the tuning system and the context.
    – phoog
    Commented Jan 24, 2021 at 17:11
  • @phoog fretless string instruments can play in different temperaments which leads to this.
    – Dom
    Commented Jan 25, 2021 at 3:43
  • @Dom my point is, if I recall correctly, that players, including fretless string players, are not going to play the note at a given frequency because it's written as a C natural or B sharp but based on what sounds good.
    – phoog
    Commented May 7, 2021 at 13:44

I would just like to clarify a couple things that I don't think have been fully articulated.

First is that there is a distinction to be understood between the concepts of "note" and "pitch". A note is a symbol in a score. It represents a pitch to be sounded. Enharmonic equivalence is idea that the same pitch can be represented by different note names. For example, the notes D# and Eb represent the same black key on the piano. What we see here is that the pitch which we are accustomed to name by the note C is named by the note B# instead. They are enharmonic equivalents.

With regard to the second part of the question, "why?": there is a reason that notes in a scale are spelled the way they are: every note in a major or minor scale has a specific function and a specific relationship to the other notes in the scale. The spellings express these relationships and functions. The function of the seventh scale degree is usually to produce a high degree of harmonic tension which urgently wants resolving.

A principle that goes along with this is that notes which introduce tension are generally resolved in specific ways. The seventh scale degree is often called "the leading tone" because in most cases it resolves up to the eighth (tonic) scale degree. It would be quite out of place to spell this note as C natural; the implications of that spelling are quite contrary to the harmonic function.

  • "a note is a symbol in a score": not necessarily. The word can also denote a tone played or sung at a specific pitch or for a specific duration, or both. Some people prefer to define "note" and "pitch" more precisely as terms of art for the purpose of theoretical discussion, but it is not incorrect to use these words with their common senses.
    – phoog
    Commented Jan 24, 2021 at 17:15

If it was written as C, it would be actually C# ... because you have four sharps on left (those ####) and they basically mean that:

  • F = F#
  • G = G#
  • C = C#
  • D = D#

Which is E major or C# minor. Instead, they write it as B# because they want you to play actual C.

It could be also written as a C with a natural sign ♮ ... the natural sign would "cancel out" the sharp # on C.


It's nothing whatsoever to do with imaginary problems in writing a C natural! It's about spelling a major 3rd above G# correctly, and making the interval LOOK like a 3rd, not a 4th.


That looks like C# minor which gets its leading tone (B) raised by a semitone. You are correct in thinking that B# and C are played at the same place but for the purposes of music theory they are not the same notes. They are what is called enharmonic equivalents ie two notes with different names played at the same place.


The main notes of a tonal scale comprise 7 pitches, each consistently designated by its own letter. So a piece in C major would generally use the pitches C-D-E-F-G-A-B-C. A piece in C# major would use C#-D#-E#-F#-G#-A#-B#-C#. It would be incorrect to designate these as C#-D#-F-F#-G#-A#-C-C#, as there would be two "flavors" of F and of C, but no "flavor" of E or of B. The piece in your example appears to be the "Moonlight Sonata", which is in C# minor. The pitch below the C# is thus written as a B#.


It is, believe it or not, simplifying sight reading. Those three notes at the start form a major dominant seventh (G♯ is the dominant to C♯ minor, and the raised third and natural seventh makes it a major seventh chord). In particular when those three notes were stacked in a single chord, the chord shape would make its function recognizable.

Now the notes are not in a single chord, but they are still fingered as a functional unit. Once sightreading progresses to a state where you don't recognize single notes but functional phrases and chords, it is much more helpful if the score reflects the function of notes rather than the particular key to press since that is more useful for letting the fingers act in patterns associated with the current scale rather than "phonetically" key by key.

That is not a universally accepted rationale: there are "piano keyroll" notations that are much more tightly coupled to the physical keyboard layout. Those notations are worse suited for recognizing patterns and musical content. For lute and then guitar, tablature notations (which again focus on physical note actuation rather than musical function of a note) remain popular as opposed to "proper" note notation.

But for most keyboard instruments (with several wind instruments also having a diatonically inspired layout of note control, partly employing transposing notation to have the central scale be C major), there is no customary notation that would be closer to the keys than standard scores with functional scales like those used by singers. And while the note spaces without accidental use follow the white keys of the piano, they are not synonymous with them.

So using the same key for the notes written as B♯ and C is really not more strange than using the same key for the notes written as F♯ and G♭.


*I'm confused as to how I should play the second note below, B#. Does it mean it's a C? Is it possible? In which case, **why is it written like this, and not just C?**

In short, the B is raised a (1/2) step to B# as an adjustment to the Harmony of the song. To understand, let's harmonize the C# minor scale using triads.

As the key signature indicates, the key of C# minor has four sharps: (F#, C#, G# and D#).

Here are the first seven tones of the C# Natural Minor Scale:

C# - D# - E - F# - G# - A - B

and the Harmony:

i. C# Minor: C# - E - G#
ii. D# Diminished: D# - F# - A
III. E Major: E - G# - B
iv. F# Minor: F# - A - C#
v. G# Minor: G# - B - D#
VI. A Major: A - C# - E
VII. B Major: B - D# - F#

Notice that the chord on the fifth (Dominant) scale degree is Minor (G# Minor).

= = =
In Music Theory, the seventh scale tone (B Natural) of the diatonic (natural) minor scale is raised a half-step in order to get a major chord on the Dominant (fifth) scale degree. Here is the scale now:

C# - D# - E - F# - G# - A - B#

The Dominant Chord is now Major:
(V.) G# Major: G# - B# - D# or (5 - #7 - 2)

This (B#) also gives us a Leading Tone into the Octave and the Harmonic Minor Scale. By Leading Tone, I mean that the ascent into the Octave is now a 1/2 step (B# -> C# ) from the (previously) whole step (B natural -> C#). Also:

  • NOTE: We now have a third pair of (1/2) steps in the scale

D# -> E (2 -> 3)
(5 -> 6) G# -> A
B# -> C# (7 -> 1)

Additionally, an Authentic Cadence (V/V7 -> I) as a resolution, in Minor, can sound very dramatic as chord tones resolve.

*IMPT: having a (B#) as the seventh degree of the scale creates these changes to the harmonized C# Minor Scale:

III+: E Augmented: E - G# - B#
V. G# Major: G# - B# - D#
vii. B# Diminished: B# -D# - F#


This piece is in the key of either E major or C# minor. The melody line goes G# - B# - F#, spelling out a G#7, a dominant chord of the III (mediant) of the scale, a secondary dominant to the submediant (VIm or C#m in this case). This harmony would be normally a G# minor having B instead of B#, but due to its secondary dominant nature it will have its third sharpened.

  • Indeed, and the way to sharpen a note is to raise it by an augmented unison. This leaves the letter part of its name unchanged; that part is still B. So the result of sharpening B is B#. To write C instead of B# would be to put it on the wrong degree of the scale.
    – Rosie F
    Commented May 3, 2019 at 8:23
  • 2
    looks like Beethoven sonata op.27 no.2 'quasi una fantasia'
    – Divide1918
    Commented Mar 11, 2020 at 3:48
  • 2
    In fact it's not the secondary dominant but the normal run of the mill primary dominant, since the piece is in C sharp minor.
    – phoog
    Commented Mar 21, 2023 at 16:51
  • @phoog you're right, I don't know why I wrote secondary back then. Commented Mar 22, 2023 at 17:11

To further confuse things, the notes may only be enharmonic (same pitch) in equal temperament. In some other temperament, they may be slightly different pitches.

  • 2
    This is incorrect. In any 12-tone temperament, and in many temperaments with more tones, they can only be the same pitch. They can only be different in an untempered context (instruments or voices that can alter tuning during performance) or in a temperament that has separate B♯ and C (for example, a keyboard with an extra key for B♯).
    – phoog
    Commented Feb 4, 2020 at 18:57
  • Is he not referring to temperaments with more than 12 tones? Though the clarification is important.
    – awe lotta
    Commented May 7, 2021 at 3:23
  • 1
    @awelotta this is a piano piece. Keyboards with more than 12 tones per octave were a relic of the distant past in Beethoven's day. And even rarer than a keyboard with split sharps is one with extra keys between B and C or between E and F. (So even in a keyboard with seventeen keys per octave there isn't going to be a separate key for B sharp and C natural, which is why I said "in many temperaments with more tones.") But the idea that Beethoven ever imagined this piece to be played in a temperament with more than 12 tones is farfetched at best.
    – phoog
    Commented May 7, 2021 at 13:53

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.