Music Theory is the study of the relationships of all pitches to each other. A single note, let’s choose middle C, by itself does not have any particular relationship until a second note is sounded either before, during , or after the chosen note. The relationship of the two notes can now be determined and a particular function can then be assigned to the chosen note. As more notes are combined the relationships become more defined along with their function. Combinations of pitches include Scales and Chords, Melody from scales, chord progressions and chord successions.
The study of Music Theory gives one an understanding of how music is constructed. Different styles of music are created by the use of particular scale and chord combinations. For example; Classical music makes use of both Major and Minor (7 note) scales while Blues and Rock make use of Pentatonic (5 note) scales. An understanding of these differences can make complex music more interesting and accessible to the listener, gives the instrumentalist a roadmap of the music they would be playing and perhaps improvising over, and provides the composer with a multitude of possibilities whether they are writing a simple song or composing an intricate piece for orchestra.