As parents and teachers, we are always looking for ways to understand our children, to interpret their behaviours, and to be able to support them more fully in their development. In Waldorf Schools around the world, it is very common for teachers to use the Four Temperaments Model, as a foundation for understanding their students. This is one of the oldest personality type systems in the world. The origins of this typology belong to Graeco-Arabic medicine, where it was successfully used to treat illnesses. In fact, it is still used today by practitioners of traditional medicine around the world. Greek physician Hippocrates (c. 460 – c. 370 BC) described the four temperaments as part of the ancient medical concept of humourism, that four bodily fluids affect human personality traits and behaviours. He believed that certain human moods, emotions, and behaviours were caused by an excess or lack of body fluids (called "humours"), which he classified as blood, yellow bile, black bile, and phlegm. The Four Temperaments are sanguine, choleric, melancholic, and phlegmatic and were coined by the Greek physician Aelius Galenus to describe the effect of these humours on human behaviour. Modern medical science does not define a fixed relationship between internal secretions and personality, although some psychological personality type systems use categories similar to the Greek temperaments.