How do you know when a note should be played sharp or flat or natural?

Answer 1

Well, first off, there's the key signature. That's the sharps or flats at the *beginning* of the line of music. They dictate notes which should be sharp or flat *all the time*. So for instance, if the song is in the key of G, there will be a sharp sign at the beginningf every line of music, on the top line of the staff (assuming treble (G) clef), to indicate that F's are sharp. Always. So every time you see an F anywhere on the staff, it should be played as an F#, even though it won't be written as an F#; it will be just written as a normal F, and you're supposed to know from the key signature that it really means F#. In addition to the sharp or flat symbols, there's also the natural symbol. This means "*don't* play the note sharp or flat*. For instance, let's say there's a song in G, which has the key signature I just described, indicating F's are always sharp. But suppose that in one instance, it really wants a normal F, an F natural-- not an F#. The way that that gets indicated is by putting an explicit natural sign next to the note (instead of a sharp or flat). The natural sign looks like a square version of a combination lower-case b and lower-case q; that is, a little square box with a tail coming off down the right side, and another sticking up on the left side. Finally, there are the rarely seen *double* sharp and *double* flat. These indicate that a note that's *already* sharp should be made *even sharper*. For instance, again, in my key-of-G example, I could indicate an F-double-sharp, which would mean take your F# and raise it *another* half step. The resulting note would be identical to a G, of course, which is why it is seldom seen. You'd typically only ever see it in a rare key such as G#. If you were in the key of G#, then *every* note would be sharp, except for F's, which would need to be *double* sharped. You'd want to call that note F-double-sharp, rather than G, because you've already got G#; Music Theory dictates that you don't want your scale to have two kinds of G but no F's of any kind. That is, if you don't call it F-double-sharp, your scale would be: G# A# B# C# D# E# G G#. Two flavours of G, no flavours of F. We'd rather have one of every letter. So we name the notes G# A# B# C# D# E# Fx G#. A double sharp looks like a little X. A double flat simply looks like two flats right next to each other. Why they couldn't have just used two sharps next to each other for double-sharp is a mystery I can't answer.

Answer 2

The key signature at the beginning of a bar will show which notes are to be played flat and sharp. There are also accidentals within a piece of music that indicate single notes that are played that don't coincide with the sharp and flat notes indicated by the key signature.

Answer 3

If there is a sharp/flat/natural sign before a note then it must be played that way. If there is a sharp/flat in the key signature corresponding to the note in question then it must be played that way.