Originally Posted by: Julian Vickers
2. The neapolitan 6th chord is usually played as the first inversion of a major chord on the b2 of the major key. It can function as a II chord before going to a V.[/quote]
While is does function as a subdominant, preparing for the arrival of the V, as Julian Vickers correctly notes, it can also function in a more "modern way" (especially in jazz & even blues & rock) as a tritone substitution for the V chord itself.
[QUOTE=Julian Vickers]
4. Voice leading is where one plays chords with the top note of the chord suggesting a melody.
Voice leading is regarding all the notes that comprise a chord or a whole piece of music as one note of a continuous "voice". As you move to the next chord you regard each note as moving to the next corresponding note in that next chord.
Say you have a C major chord spelled low to high: C, E, G,
Then the next chord is G major spelled low to high: B, D, G
The bottom "voice" moves from C to B, the middle voice moves from E to D & the top voice remains stationary at G. Notice that the bottom voice moves down a half step, middle voice moves down a whole step (direct motion between these 2 - down in the same direction) & the top voice being stationary is oblique motion to give it even more variety. Keep in mind that minimal movement is not always the "rule" or "goal" but it helps to think that way to start with when you are learning.
If I just moved from a C E G up or down to a G B D, then all of my voices would merely go up or down a fifth (not to mention a great deal of "voice crossing" which can be bad depending on the context). I would have no independent voice motion & thus no justification for using more than one note at a time. The other voices would be merely "shadowing" or "mimicing" not voices in their own right.
"Smooth" voice leading is the "goal" of well-constructed music. This is a VERY simple example but it is the basic idea & has amazingly far reaching implications.
Many theorists & composers also regard voice leading as not merely a chordal analysis tool but an essential way of creating independent & yet interweaving melodies. This is very true in Baroque (Bach), Classical (Beethoven) & much Romantic (Brahms) music. For although at any time you can isolate a chord based on all the notes that are sounding at one time the more important thing is that each voice carried it own melodic thread. So if you have (like Bach did in many of his classic 4 part chorales) a piece that all the way through uses four note chords it is constructed in a way that if you follow say the top note of every chord ("the top voice") you will find a complete melody; & likewise for the other 3 voices.
