A scale is simply a collection of notes that make up a musical work or passage. What makes one type of scale different from another is the intervals between the notes that make up the scale. The way in which scales are used in the music we hear today is somewhat complicated but their origins lie in the modes of ancient and early music. In early music such as the gregorian chants of the middle ages, only certain notes (or more precisely, intervals) were allowed and certain conventions governed how these notes should move in relation to one another and to the music as a whole (for example, phrases had to begin and end in a certain way). This resulted in what we call modes. There have been a vast number of musical modes throughout history and around the world. In Europe during the middle ages and renaissance there were six in common use. They were named after, but were different to, the modes of the ancient Greeks. They are the Ionian, Dorian, Phrygian, Lydian, Mixolydian, and Aeolian.
Around the the 18th century composers began to settle on just two of the modes, the Ionian mode which had a Major 3rd, 6th, and 7th above the root note, and the Aeolian which had a Minor 3rd, 6th, and 7th above its root. These two scales provided composers all the expressive possibilities they needed and came to be know as the ‘Major’ and ‘Minor’ modes. The notes which made up these modes are what we call scales.
Since the inception of the major and minor scales, many more have been used in musical composition some of these were borrowed from various music traditions from other parts of the world, in particular the pentatonic scales of Asia, and some are what are know as synthetic scales – alterations of traditional scales invented by individual composers or particular schools of composition.
Follow the links below for more about the various types of scale.