The Tonal Centre is an interactive site for music composers and theorists which explains and demonstrates some of the key concepts of tonality; including chords, scales, cadences, and modulation. Most of the musical examples are illustrated with a midi file - just click on the relevant link to hear it.
The site should be of use to any composer who wishes to expand his knowledge of tonal and scalic resources beyond that which is found in most conventional music theory publications; and for the music theorist it should provide a valuable resource of information and ideas which can be used for further exploration.
Tonality is a word that has been given many definitions, and most of these are very broad - but that is because it is a concept which is easily obscured by its subtelty, and forgotten because of its pervasiveness. Here is my attempt at a definition:
Tonality describes the relationships between the elements of melody and harmony - tones, intervals, chords, scales, and the chromatic gamut; but particularly those types of relationship that are characterised as hierarchical, such that one of the elements dominates or attracts another. These relationships occur both within and between every type of element, making a complex weave between a tone and its melodic, harmonic, and chromatic contexts. When this weave is coherent and stable we have a tonal system which is coherent and stable. The major and minor scale systems and the part that they play as members of the chromatic gamut is one such system.
In its most conventional sense, tonality refers to just the major and minor scale types - scales whose elements are capable of maintaining a consistent set of functional relationships. The most important functional relationship is that of the tonic note and the tonic chord with the rest of the scale. The tonic is the element which tends to assert its dominance and attraction over all others, and it functions as the ultimate point of attraction, rest and resolution for the scale.