The b and the # are known as accidentals . In western music there ' s twelve notesPitchclassspace . svg . png . Scales are built from creating a pattern and the notes that fall in that pattern . Check the followingThe distance between notes in semitones is known as an interval , since there are twelve notes , there are twelve intervals , as shown in this diagram . For example , the major scale uses the intervals shown in this diagram , the natural minor scale uses the intervals in this diagram . The same applies for every other scale . Now , let ' s layout the twelve notes with a scale diagram over it . For example , let ' s choose G as our root and layout the major scale pattern above it . What are the notes ? I ' ll give you some time to figure it out . Done ? The notes are G A B C D E F #. If your questions was more in line with why sometimes b is used instead of #?, I also have the question . In the traditional musical system , to write a scale you do the following . You write down the seven notes but without accidentals . Then you add the accidentals . If you used b , then all your accidentals must be typed with b . If you used #, then all your accidentals must be typed with #. Learn about the circle of 5 ths to see the patterns that arises from adding accidentals .