Psychology is considered a science - a science with a special focus on behaviour. (psychology the science of behaviour 4e, 5) Discovering and explaining causes of behaviour (why people do what they do) is the primary focus. There is a lot of emphasis put to this when explaining psychology. The word psychology is derived from two greek words: psukhe meaning breath or soul and logos meaning word or reason . The modernized meaning of psyucho- is mind and logy is science . If we can discover the events that caused the behaviour, we have explained it (5) Casual events: events that cause other events (including behaviour) to occur. An important reason for studying human behaviour is that human behaviour is the root to many of the world"s problems (i. e. poverty, war, terrorism, crime, and etc. Physiological psychology examines the physiology of behaviour (6). The organism"s physiology especially its nervous system is taken to be the appropriate level of reason/explanation.