There are 12 semitones on a musical scale There are 12+ loaves in a baker's dozen (the exception that proves the rule) The point on #5 is critical. Before we

There are 12 semitones on a musical scale There are 12+ loaves in a baker's dozen (the exception that proves the rule) The point on #5 is critical. Before we had a solid currency system or notion of debt, we commonly had to divide things up from a group. 12 gives a lot of flexibility in that regard. In fact, selling 12 units of something became so common that certain industries added an extra unit just to be sure that the number 12 was given (baker's dozen).