Major scales are made up of the intervals tone-tone-semitone-tone-tone-tone-semitone. In other words, the semitones are between the third and fourth scale degrees and between the seventh and eighth degrees. Learn more about tones and semitones here. Below is the major scale in A. Note that there are three sharps in the A major scale (F sharp, C sharp and G sharp).
Below is the F major scale. Note that this scale uses flats instead of sharps. It was necessary to add a flat sign (on the note B) to keep the interval between the third and fourth degrees a semitone.
We add a key signature at the beginning of each line of the staff to indicate to the player the key of the music (i.e. the scale being used in the piece). Below are what the key signatures of the scales above look like when written on a score:
It is important to remember that sharps and flats are placed in a fixed order on the staff. So, in the case of A major, F sharp is written first, then C sharp and finally G sharp. Click here to read a more comprehensive explanation of how key signatures work and to see charts showing you all the major and minor key signatures.
More on Keys
Working out the key of a piece of music is easy if there is a key signature. But, what if you come across a musical excerpt where the key signature is not present and there are only accidentals? The melody below uses 1 accidental (B flat). Therefore it is in F major.
Besides accidentals, make sure to also check the first and last notes of the melody when deciding the key of the piece. Melodies most often end on the keynote (also referred to as the tonic). For example, the melody below, uses only 2 accidentals (F sharp and C sharp). At first you might conclude that it is in D major because the scale of D major only has 2 sharps (D major scale consists of the notes D-E-F sharp-G-A-B-C sharp-D). However, if you look in detail, you will notice the melody starts and finishes on the note A. It just so happens that the melody does not include the note G sharp.
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