Technicist penology merges with mainstream criminology in that the advice it offers is often based on the beliefs of mainstream criminology about the causes of crime and the nature of people who commit crimes. Ideas about the gradation of punishments which were the foundation of so-called 'classical criminology' of the eighteenth century were thus based on the idea that crime was rational behaviour, an idea which is in favour again now, whereas the 'positivist criminology' of the nineteenth century and the first two-thirds of the twentieth was based on ideas of people's behaviour as being determined by circumstances or by psychological or physiological predisposition. Contemporary ideas about additional imprisonment, or refusal of parole, for prisoners likely to reoffend, as well as suggestions about how to help people refrain from reoffending while dealing with them by community penalties such as probation, all derive from current crimi¬nological notions about the causes of crime.