This chapter looks at things determines what we do about measuring or changing those things; be it the problem child at school, racial prejudice, disturbed behaviour in the individual, or that indefinable concept ‘personality’. The person as an entity has been hooked on to the categories as an afterthought as in ‘person perception’; or has been equated with their ‘reinforcement history’; or has been regarded as a source of error variance sometimes annoyingly encountered when one is trying to measure generalities scientifically. G. A. Kelly never makes explicit his definition of the term ‘personality’, but he repeatedly implies that our personality is our way of construing and experimenting with our personal world. C. L. Hull’s theory of learning, for instance, broke down when attempts were made to extend it to cover personality. A more cognitively complex person has available a more differentiated system of dimensions for perceiving others’ behaviour than does a less cognitively complex individual’.