Harmony/Intro to Voice-leading
Voice leading is the linear progression of individual melodic lines (voices or parts) and their interaction with one another to create harmonies. Imagine a choir with 4 voices: each voice is singing a specific melodic line of music. Harmony is concerned with what the lines sound like together, while voice leading is concerned with how the individual lines develop.
"Good" vs "Bad" Voice Leading edit
Although formal conventions exist in different music cultures, a simple indicator of good voice leading is that all the parts of polyphony in a piece are easy to sing and/or sound good independently.
Types of Motion edit
Static motion is almost always desired if it's harmonically possible. The pitch of the note is unchanged from the previous note. It is the least musically demanding development possible in a line of music aside from a rest.
Stepwise or Conjunct
After static motion stepwise motion is the next best option in terms of voice leading because it requires very limited musicianship: an understanding of the scale and the ability to identify the type of motion.
Skipwise or Disjunct
If independent melodic motion is not static or stepwise, than it is disjunct, or it "skips." In terms of good voice leading, disjunct motion is avoided if possible because it can make the line difficult or confusing, and it can also sound awkward.