What is Music?
To the point... Music is organized sound.

By this definition, for something to be considered music it must have only two elements:  
Sound (of some sort)
Organization (of some sort).  

This definition allows us to consider all types of music from ancient to modern, no matter what the sound source or the type of organization (structure).  It also helps us avoid imposing opinions or personal tastes into the formula, which might exclude certain types of music.

What is Harmony?
Harmony is the simultaneous sounding of two or more pitches.

It is the vertical aspect of music -- but is often the resulting combination of the components of horizontal movement.  (See the example below.)

What is Tonal Harmony?
The term generally refers to the harmonic style of music composed from around 1650 to 1900, although aspects of tonal harmony can be seen much earlier and much later.

Works based on Tonal Harmony have several characteristics:
    •     They make use of a tonal center -- a pitch class (a specific pitch without octave designation) that provides a harmonic center of gravity
    •     They use major and minor scale forms almost exclusively
    •     They use chords that are tertian (built in thirds) in structure
    •     Chords in tonal music generally serve a functional role in the harmonic structure

What is Functional Harmony?
It is a harmonic structure in which the chords relate to each other, and the tonal center, in specific and often complex relationships.

The chords "function" in different capacities within the tonal framework.  Certain chords "lean toward" other chords (as can be heard in the V7).  Their particular sound, within the framework of a tonal center, creates an anticipation in which the listener "expects" a certain progression or resolution.
Examples of Tonal music can be found in the works of: