ABSTRACT
Medieval theorists classified interval sound into three categories: Perfect Consonance, Imperfect Consonance, and Dissonance. We can use this categorization to simplify the identification of intervals. Consonant intervals and imperfect consonances are stable. They do not need resolution. Dissonant intervals are active and they need to resolve their tension by expanding or contracting to another consonant interval. This chapter treats the perfect 4th as a perfect consonance. An inverted interval stays within its category. For example, a 3rd inverts to a 6th, a 7th inverts to a 2nd, a 5th inverts to a 4th and so on. The only thing that changes in inversion is the interval quality; for example, a minor 3rd inverts to a major 6th, an augmented 4th inverts to a diminished 5th and so on.
