Music theory books are an important part of the musician's arsenal, because they explain and expand all the fundamental elements which music is constructed on. To become a proficient musician and composer, it's important to have a thorough understanding of musical terminology. Performers will benefit from the deeper level of understanding of the works they are performing, and composers can use theory to give their musical ideas a strong and effective framework.

Below is a list of the typical topics that will be covered in a standard music theory text:

Definitions (pitch, interval, scale, inversion, key, time     signature, rhythm, consonance, dissonance,     enharmonic, diatonic, chromatic, appoggiatura).

Chord Types

Voice Leading

Harmonic Functions

Chromatic Harmony

Suspensions, retardations and Anticipations.

Non-chord Tones

Counterpoint

Secondary Domonants

Augmented Sixth Chords

Neapolitan Sixth Chord

Modulation

Cadences

Figured Bass

Polyphony

Fugue