Comparable parts is a concept found in Sally Swift's Centered Riding. The idea behind comparable parts is that what we do in a specific area of our body directly affects that comparable (equivalent) body part of the horse. One time during a Centered Riding lesson I focused on relaxing my tongue without being told to do so. My instructor was watching the horse and not me. "What did you just do? He just relaxed his mouth!" she said, and this is when I truly learned the power of comparable parts.
Self-carriage is a term you will hear often in horsemanship, and it can be defined in many ways by many different people and disciplines. Commonly it is defined by the horse having a rounded back and engaged hind-end with the weight being shifted toward the hind-end causing lightness in the forehand.
Okay.... So how does this all come together?