In short, psychology overlaps with many other areas of study or even areas of life and work. Perhaps in part because of this, a defi nition has proved diffi cult for more than 100 years. Nowadays, it is usually defi ned as: the scientific study of behaviour and mental processes. Some years ago, behavioural purists wanted the defi nition to embrace only behaviour, but the vacuity of that was eventually realised. There is clearly more to the human condition than behaviour. Also, the word psyche has an interesting background; it is a mixture of mind, spirit and, originally, even air (the other sense of spirit).