‘It is sometimes argued that economics cannot be a science because it studies human behaviour and human behaviour cannot be reduced to scientific laws’. There is an element of truth in this. It is very difficult to understand and predict the behaviour of individuals. However, nearly all economics is based on the study of the behaviour of a group of individuals- the behaviour of groups is often far more predictable than that of individuals. Moreover, we tend to judge a science on its ability to establish laws which are certain and unequivocal. But even in a hard science such as physics, it has become apparent that some laws can only be stated in terms of probabilities.