Are accidentals written as sharps or flats in the key of C?

Question

The title of my question pretty well encompasses the entirety of it. It falls outside the realm of sticking with the key signature as it is neither sharp nor flat.

Answer 1

Both. In a fragment of a chromatic scale, 'sharps going up, flats coming down' is a pretty good rule (and one which applies beyond C major, even in a 'sharps' key signature we wouldn't force a downward chromatic phrase into sharps).

Where there's triad-based harmony, choose accidentals that make it clear. F minor and E major are both common chromatic chords in C major. It would be ridiculously unhelpful to spell the former with a G♯ or the latter with an A♭

Answer 2

You can find both. It depends on the tonal context. If the accidental is bringing a minor tonal color to the piece, it is probably a flat. This would normally be a lowered third, seventh, or sixth degree of the scale (E♭, B♭, or A♭). The lowered seventh degree can also be found in a harmonic move to the subdominant (i.e., a B♭ creating movement towards F major).

On the other hand, the concept of "secondary dominant" describes the tendency to raise a scale degree to make an intermediate cadence on a pitch other than the tonic. An example that comes up here occasionally is the Star-Spangled Banner, where the pitch of "‑ly" in "dawn's early light" is raised, so it would be an F♯ in C major, because there is an intermediate cadence on the fifth degree (G) on the word "light."

So in various contexts there will be different answers. You can have an E♭ from a "borrowed" C minor chord and a D♯ serving as the third of a secondary dominant B major chord that leads to E.

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For a real-world example, consider Begin the Beguine. It has been published in B♭ but the original key is C. In the bridge, it moves to the parallel minor, so there are lots of flats, but near the end there's an A major chord, which means there's a C sharp.

The rule that flat-side key signatures demand flats for accidentals, and the same for sharps, is also ill conceived. If you transpose Begin the Beguine to G major, with a key signature of one sharp, the flats in the C major version are all still flats except for the B♭, which becomes F♮. Conversely, if you transpose it to F major, with a signature of one flat, the C♯ that was the third of an A major chord in the original key becomes a C♯, the third of a D major chord.

In deciding how to spell your accidentals, a better approach is to consider the immediate harmonic context (i.e., the current chord) rather than the overall tonality.

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In a comment you write

There are two instances in which I make use of accidentals in one piece that is written in C. The first moves from a G to what I notated as an A sharp and, then, to a C. That occurs twice in the piece. The next instance is where I move from an A to what I notated as a B flat to a C. I guess I should change the B flat to an A sharp?

More context might lead to a different answer, but typically an interval of two half steps should be spelled as a major second, using adjacent letters of the alphabet (or G and A). This suggests that these are both B♭s. An A♯ would normally ascend to a B(♮) or perhaps a C♯ or D♯. There are however harmonic contexts where A♯ to C makes sense, but it would be unlikely to find such a context in the key of C. (Furthermore, the most obvious such context would only be spelled with A♯ in classical theory where it is called the "augmented sixth chord"; in jazz theory and related modern theoretical frameworks it is called "tritone substitution" and the augmented sixth is spelled as a minor seventh, so the A♯ is instead a B♭. This tells you that there will be some cases in which the answer won't be clear-cut, but don't let that make you think that this is true of every case.)

Answer 3

There is only a loose rule stating in a flat key accidentals will be flats, and in a sharp key, accidentals will be sharp. There's also the 'rule' about making music easier to read. Which often involves using as few accidentals (including cancelling naturals) and that may well contradict the previous 'rule'.

Then there's the reflection of the accidental note on the chord underlying it. That's the awkward one for me: I often see, for example, a chord with an altered note that should be sharpened, (reflecting the name), but has the note one tone above flattened instead.

So, there is no hard and fast rule , not only for key C, (or C minor), but any key at all. The guide that should be paramount is - write an accidental note so it (and the following note/s is easiest to read. But I would expect. for example, to see G♯ where there's a C+ chord, but its enharmonic A♭ where there's an Fm.In key C, or any key. Seems more logical, although it isn't always followed.

Answer 4

Where applicable, go with the chord. If the harmony is Fmi, write Ab; if E7, denote the same pitch as G#.

This goes for any key. In G minor with its two flats, there'll likely be D or D7 as the dominant, containing F#. So you write it as F# in the melody line as well. Gb just wouldn't make any sense there.