Multiplexing is information management.
For Edison, it was sending more than one telegraph message down a wire at the same time. In music, it is combining several lines of information in such a way that they can be followed independently. For harmony to exist there has to be more than one message in transmission. The art of harmony lies in encoding multiple messages so that they do not interfere with one another in transmission and may successfully be decoded as separate strands by whoever is at the receiving end. The art of harmonization nevertheless implies a horizontal dimension, the management of multiple layers of information over an extended period, and the rules of harmony are designed to ensure that a balance is maintained between separation of individual lines and harmonic consistency within the group.