When we say music theory, we usually aren't talking about a universal system of understanding music. Rather, we are focusing specifically on Western Tonal Harmonic music, or "common practice" music. This type of music was developed from 1650 to 1900 in Western Europe. We consider it "common practice" not because it is the only good sounding music, but because it was a widely accepted system of analyzing music for three hundred years and is the foundation for much classical, pop, rock, and some aspects of blues and jazz music.
Let us define this type of music theory a little further. Music theory is merely a system of describing, notating, communicating, and analyzing music. It is not a "theory" like the theory of relativity, but rather a framework for understanding many types of music. It does not describe how music should work or what makes music work, but is simply a method by which composers, musicians, educators and anyone else can communicate and understand Western Tonal music.
While there are certain advanced elements to music theory (such as tuning and the overtone series) which have a "universal" application due to being based on the physics of vibration, the more common elements of music theory that are taught in universities today are these aspects of Western Tonal Harmony. The music theory we discuss here would not be particularly suited to talking about Indonesian Gamelan music or very modern classical pieces, both of which would require a different method of music theory analysis.
Pitch
All music is based on sound and when we refer to a specific tone we are referring to a pitch. Every key on a piano plays a different pitch. In traditional western music, we focus on twelve pitches to make music. They are as follows:
If you've seen a piano before, you'll notice that after we get to B, the whole thing just starts over again. Normally, there are eight C-keys on a piano. Each of those keys plays the same sound (in this case, the tone C) but higher or lower depending on the key. Therefore, we would say that the eight C-keys on a piano are the same pitch class but differentpitches.
If you consult our pitches above, it may appear that seventeen notes have been listed, but this list actually only contains twelve notes. The notes with a slash between them areenharmonic, meaning that they represent the same pitch with two different names. For example, C♯ (C sharp) and D♭ (D flat) are actually the same. To see this, these notes both get played by the same black key on a piano.
The sharp and flat symbols should be familiar to you by now, but let us have a quick review. A sharp is one pitch higher than the note it is attached to. For instance F♯ (F sharp) is one pitch higher than F. Inversely, a flat is one pitch lower than the note it is attached to. Thus, E♭ (E flat) is one pitch lower than E. You might be tempted to think that any sharp or flat is the same thing as a black key on the piano, but this is not so. For instance, E♯ is enharmonic with F and C♭ is enharmonic with B.
While they are not quite as common, there is also a double sharp (x) and a double flat (♭♭). These symbols only mean that the tone is two pitches higher or lower than the note they are attached to. For example, A♭♭ would be enharmonic with G and Dx would be enharmonic with E.
The majority of Western music has emerged from the twelve pitch classes listed above. Just about every Western scale and chord (and a great many non-Western scales and chords) are founded from these notes.
