Blood, Bile and Phlegm
To the ancient Greeks, the ways in which a person behaved were an integral part of their general health. They believed that the body contained four fundamental liquids (called humors) based on the four elements of fire, air, water and earth. When one of these humors became dominant over the others, it was thought to effect the person's mood and general approach.
The four humors, blood, yellow bile, phlegm and black bile, were each believed to be responsible for a different type of behavior. An excess of blood made a person sanguine, yellow bile resulted in a choleric style, phlegm, naturally, produced a phlegmatic outlook, and black bile was associated with melancholia.
These theories, first set down in a systematic way by Hippocrates, remained in use until the middle ages. We now know, of course, that they have no basis in medical fact, but what the Greeks had almost incidentally achieved was the first systematic method of describing individual types. So successful was their approach that, even today, the words 'humor' (meaning 'mood'), 'sanguine', 'phlegmatic' and 'melancholic' are still in common use.
Thankfully, the DISC system does not rely on measuring the amount of yellow bile in a candidate to determine their behavioral style, but the ideas behind it can, indirectly, be traced back to Hippocrates' theories.
Carl Gustav Jung
There are many modern theories of behavior based on the idea of four factors. Perhaps the most influential of these is to be found in the work of the Swiss psychologist, Carl Gustav Jung. He defined individual behavior as belonging to one of four different types; Sensing, Intuitive, Feeling and Thinking.
The definitions of these types are rooted in Jung's lifelong work on the unconscious mind, and need not concern us here. They are important because they represent one of the first serious attempts to map the human psyche by a modern psychologist. Assessment tools based on Jung's work are still available today.
It was Jung's opinion that people instinctively understand behavior in terms of a set of four elements (his four types being one example of such a set, and the four humors of the Greeks being another). These groups of four (technically called tetralogies) underlie a very large number of assessment techniques, and DISC is no exception.
The Emotions of Normal People
In the early 1920's, an American psychologist named William Moulton Marston developed a theory to explain people's emotional responses. Until that time, work of this kind had been mainly confined to the mentally ill or criminally insane, and Marston wanted to extend these ideas to cover the behavior of ordinary individuals.
In order to test his theories, Marston needed some way of measuring the behavioral styles he was trying to describe. His solution was to develop his own technique to measure four important factors. The factors he chose were Dominance, Influence, Steadiness and Compliance, from which the technique takes its name - DISC.
Marston published his findings in a book entitled The Emotions of Normal People, which included a brief description of the system he had developed. From these humble beginnings, the DISC system has grown to become probably the most widely used assessment tool in the world.