Scales are invaluable tools by which to refine articulation and reinforce dexterity. For these reasons, most guitarists’ practice scales for these purposes, without realizing the superficiality of their drill. Although scales do exercise and improve articulation, increase dexterity, and allow greater fluency, they may provide much more such as a deeper understanding of key signatures, composition, arrangement and, of course, soloing. The simple practice of scales for the sake of the same is cursory, where the study of them is inestimable.
For this reason, scale theory should be studied, and the comprehension of this theory unlocks a whole new world within a world. Scale theory is a constituent of music theory it is a specific discipline within a broad abstract.
Because of the complexity of music theory, there are many subcategories thereof, and these subcategories become complex in and of themselves. Scale theory, to be sure, is not unique; chords may be broken down and studied much the same way, yielding yet another facet of music theory – chord theory.
One can never truly come to a whole, comprehensive understanding of all music theory for these reasons. As music continues evolve and be redefined (as well as new genres surfacing), one can only obtain a general or broad cognition of the abstract, therefore most musicians study one facet within one specific genre. Because of this, most musicians are unaware that there are indeed aspects of music theory not typically scrutinized in traditional study.
A scale, in the most convenient definition, is an arrangement of a series of intervals or tones. These intervals are simply, the step from one note to the next. The smallest step (for the purposes herein) is a half step or semitone. (The half step is the smallest interval in Western music with the exception of the unison in Eastern music, the steps are divided further into quarters). On a piano, the half step or semitone is the step between one ivory key and an ebony key (or another ivory key if not separated by an ebony key) and the step from one fret to the next on a guitar. The step from one ivory key to the next on a piano (if separated by one ebony key) is a whole step or whole tone and the step between two frets on a guitar.
These intervals are based on the seven natural notes and the steps between them. There is a whole step or whole tone between each of the seven natural notes with the exception of B to C and E to F, which are only one half step or semitone. (Again, this is applicable to Western music, as more notes are recognized in Eastern music because of the interval division).
In order to form a scale; the intervals or steps are arranged to yield a specific tonal quality and accord within their respective key signature this signature being relative to either Major or Minor. As you will observe, these scales share the same intervals (number of sharps # or flats b) as their respective key signature.