The original diatonic scales had seven letters of the musical alphabet (C, D, E, F, G, A, B). Repeating the keynote at the end of the scale makes the scale sound complete. Thus, scales typically include eight notes (C, D, E, F, G, A, B, C).
There are seven types of diatonic scales, each of which begin on different keynotes and have half steps and whole steps in different places. However, the most popular diatonic scales used in Western music are the Ionian and Aeolian scales. The Ionian scale is known as the major scale. The Aeolian scale is known as the minor scale. The major scale has a half step between the third and fourth notes and also has a half step between the seventh and the eigth notes of the scale. The minor scale has a half step between the second and third notes and also a half step between the fifth and the sixth notes of the scale. Below are examples of the C major and A minor scales.
What happens if we wish to build a major scale on G? First list the notes on a staff and follow the rule. We need a half step between notes three and four and also a half step between notes seven and eight. Here is what you get:
What happened to the seventh note of our scale? We know we need a half step between notes seven and eight, so we made the seventh note sharp. Thus, we conform to our rule that major scales have half steps between notes three and four and also between notes seven and eight.
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