# When is a note flat/sharp?

For instance we are playing a B, is the third note of the chord a Eb or and D#? If we play Bm is the fifth a Gb or a F#?

This is one of those questions that seems really obvious once you have a decent amount of experience, but can be a little challenging to explain.

I'm going to try and give you a couple of approaches that might help. All of the three ideas below are explaining the same thing from different starting points. Hopefully one of them makes sense.

After the first section, I've written a few quick comments on other connected ideas, or questions that might result from the other sections.

First idea. Are you familiar with your key signatures? Key signatures always have flats or sharps; never a combination of both. If our chord progression stays entirely within the key signature, we get an easy shortcut. If the key signature has flats, you're going to spell everything as a flat, not a sharp. If it has sharp, you're going to spell everything as a sharp.

Let's take your example. The key of `B Major` has five sharps. So, we're going to spell the accidentals as sharps, not flats. Which means the notes are D# and F#.

What about `Cb Major`? It has seven flats. Now, if you play this scale, it will sound the same as `B Major` (ignoring temperament, which is superfluous to this discussion). We're going to spell the accidentals as flats, not sharps. Which means the notes are Eb and Gb.

Second idea. Every major and minor scale has seven notes. Each of those notes has a name; it's a letter, and sometimes an accidental. Within the scale, we want to make sure that every note has a different letter. We don't want to be seeing Eb and E in the same scale; it makes things messy.

Back to your example. Following this single-letter rule, we can only spell it:

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

If we try to use Db instead of C#, we won't be able to complete the scale without repeating a letter somewhere, unless we spell the B as a Cb. But that's a `Cb Major` scale, not a `B Major` scale.

Third idea. Intervals. Each interval will have an associated letter. In a B scale:

• The second will be some sort of C
• The third will be some sort of D
• The fourth will be some sort of E
• The fifth will be some sort of F
• The sixth will be some sort of G
• The seventh will be some sort of A
• The octave/unison will be some sort of B

So, the third must be a D#. It can't be an Eb, because that would be a fourth of some type (diminished, specifically). You can apply this pattern to any scale.

Notes and Chords. This all applies equally to both notes and chords of a scale. The third note of `B Major` is called D#. The third chord of `B Major` is called `D#m` (hopefully it's clear why it's a minor chord; if not, comment). The fifth of `B Major` is called F#. The fifth chord is called `F#` [major] (not `Gb` major).

On guitar chord charts. There's a tendency online for chord charts to refer to `Bb` as `A#`, and `Eb` as `D#`. That's ok, if the piece is in a key like `C# Major` or `F# Major`, because those are the correct spellings. It's not ok if the piece is in `F Major` or `Bb Major` or `Eb Major`. Here's some examples:

`F` `Dm` `A#` `C` (we're in `F Major`/`D Minor`, the key signature has one flat, so it should be `F` `Dm` `Bb` `C`)

`Fm` `D#/F` `A#` `Fm` (we're in `F Minor`/`Ab Major`, the key signature has four flats, so it should be `Fm` `Eb/F` `Bb` `Fm`)

On 'weird' keys. You may already know this, but once you get up around five, six and seven flats/sharps, you can pretty much choose between a flat key or a sharp key, and it will work either way. That's cool, and confusing.

The equivalences you're most likely to encounter are:

• Five Flats == Seven Sharps (`Db Major` is the same as `C# Major`)
• Six Flats == Six Sharps (`Gb Major` is the same as `F# Major`)
• Seven Flats == Five Sharps (`Cb Major` is the same as `B Major`)

There are other equivalences, but let's not muddy the waters. You can also argue that these scales are not technically the same, but I think that's going way too far for this discussion.

How do you choose the right one? It's pretty much up to you, but you must be consistent. If you're going to call it `C# Major`, you can't use `Ab` chords. They are `G#`s. No mixing and matching.

Out of Key Signature Chords. Still with me? One last point. Sometimes a chord progression uses chords that aren't actually in the key signature. This means you need some extra accidentals. In this case, prefer flats if the key signature already has flats, and sharps in the opposite case. But this isn't as clear cut, and it depends on the chord progression. As you gain experience, you'll learn that people expect to see `Bb` chords in `C Major`, not `A#` chords. There are other theoretical reasons for these conventions, but this answer is far too long already, so I'm going to stop typing now.

• One of the most common accidentals occurs when a dominant chord is required in a minor key. The 'sharpened 7th' of the Harmonic Minor scale. And it WILL be a sharp. Or at least a natural. But not a flat. Commented May 11, 2018 at 14:55

You've answered the question by calling the intervals a 'third' and a 'fifth'. Whether perfect, major, minor, dimininished, augmented or anything else, a 'fifth' encompasses five letter names. If the root is some sort of B, the fifth will be some sort of F.

B, C, D, E, F.

1, 2, 3, 4, 5.

A fifth.

B, C, D.

1, 2, 3.

A third.

• I don't quite understand. Okay.. What about chords? It it an Ebm or an D#m and F#maj or Gbmaj? and in this chords are the notes sharps or flats? Commented Jan 13, 2017 at 18:50
• In normal equal temperament, Gb major and F# major are the same chord. The notes of Gb major are Gb, Bb, and Db, in F# major they are F#, A#, and C#. As Laurence said, the spelling of a triad by root/third/fifth is conventionally followed. Commented Jan 13, 2017 at 19:14
• Same difference with chords. Or (8 note) scales, come to that. If you root a triad on E - any flavour of E - the notes will be spelled E, G, B. If you start a scale on F, the notes will be spelled F, G, A, B, C, D, E, F. If this requires sharps, flats - double-sharps and flats even - so be it. That's how the basic spelling goes. In extreme cases, we can cheat. But be AWARE it's a cheat! Commented Jan 13, 2017 at 20:36
• @ScottWallace is there any 12-tone temperament in which Gb major and F# major aren't the same chord? Commented Jan 14, 2017 at 8:37
• @phoog- not that I'm aware of. Gb major and F# major are as two peas in a pod. Cheers from cold Vienna, Scott Commented Jan 14, 2017 at 14:58

Try not to mix sharps and flats.Start a scale with whatever note. Count up, in order, T,T,S,T,T,T,S. T=tone, s=semitone. Use the next letter for the next note.

So, in C (no b or #) the order is C D E F G A B. Start on Eb. The order is Eb F G Ab Bb C D. The TTSTTTS is the same. The letter names are alphabetic. It works simply.

Now, to answer. Your B - third letter up - D. It's 2 tones up, so it must be D#. Any sort of E would be 4th.This is fairly straightforward elementary theory, but without it, nothing after will make any sense.

The interval quantity is always determined by counting the notes. In the key of A: A=1, B=2, C=3, etc.

So if you're in the key of B, all thirds will be some type of D, and all 5ths with be some type of F.

Once you have the interval size, then you determine its quality - sharp or flat, major/minor/perfect/augemented/diminished - depending on the root and the context.

So:

So, if for example, your tonic is B:

D# is the Major 3rd. (two whole tones from the root) Eb would be a Diminished 4th (one semi-tone below the Perfect 4th, E). D# and Eb are called enharmonic equivalents: Different spellings for the same note/pitch.

F# is the Perfect 5th.(3 1/2 whole tones from the root) Gb would be a Diminished 6th (one semi-tone below the Minor 6th, G) - again, enharmonic equivalents.

Rather than asking "when is a note sharp or flat" the question is more like "how to choose between enharmonic equivalent choises?"

For instance we are playing a B, is the third note of the chord a Eb or and D#? If we play Bm is the fifth a Gb or a F#?

For that particular choice of enharmonic equivalents the thing to understand is those kinds of chords are tertian which means they are built of a stack of thirds.

The gamut of letter, without sharps or flats, in thirds is `A C E G B D F A C E...`.

So, a chord rooted on `B`, any kind of tertian chord, will be from the stack of thirds `B D F A C E G B`.

If you already know your choices for the third are between `Eb/D#` and the fifth between `Gb/F#`, then that combined with the tertian stack of `B D F` let's use know the chord is `B D# F#`.

You can arrive at the chord a different way using fundamental information about intervals and chord types. Intervals are named first by a number for the space of the letters, ex. `B D` is a third, and then the specific quality by half steps, ex. minor thirds - `m3` - are three half steps and major thirds - `M3` - are four half steps, and fifths are five letters apart, ex. `B F` and perfect fifths - `P5` - seven half steps `B #F`. Major triads are a root, ex. `B`, and a `M3` above the root `D#` and a `P5` above the root `F#`.

You are dealing with the issue of enharmonic tones in the 12TET tuning system versus the standard naming convention in music.

The Major scale in any key will have the following pattern of steps:

(W - W - H) - W - (W - W - H)

W = whole step, H = half step. There are 8 notes including the octave, 7 intervals. The parenthesis separate Tetrachords. The Maj scale is 2 tetrachords separated by a W.

The naming convention for any and all scales is determined by taking 7 consecutive letter names from the alphabet, repeating after G:

A B C D E F G A B C D E F G A B C ...

And applying sharps or flats as needed to get the correct sequence of W and H. The "degrees" of the scale are just the numbers 1 through 7 starting on the first note (not very exciting). The correct letter name for a degree is obtained by mapping the degrees to the letter string, or simply counting up from Do, starting at number 1.

In the Key of A the 3rd must be a C, in fact it is C#, but NOT Db despite the two having identical frequencies on a piano or other equal tempered instrument. In your example, B, the third note would have to be names D, since it is 3rd in the sequence (B, C, D, E, F, G, A), and it does need to be # to get 2 W space between B and its 3rd. In Bmin the 5th is determined by the same logic, the 5th letter name in the sequence is F, so it must be named F something (in this case F#).

For equal temperament a C# and a Db might be the same note but from a music theory point of view you could not say that the Db is the Maj 3rd of A. That would get points off on a theory test (I know from personal experience).