Positivism is an epistemological position or a theory of knowledge which assets that science is based upon theories that have been induced from and only from empirical evidence or the evidence of the senses (hence the term empirical or that which can be experienced by the senses). Positivists reject any evidence that cannot be objectively experienced or observed such as that derived from tradition, faith, magic, religion, philosophy or any other form of knowledge or belief that does not have an empirical basis.
Thus they want to explain criminal behaviour by reference to causes that can be observed or measured. Causes have to be material and observable biological positivists look at biological observables such as anatomical abnormalities, identifiable genetic or gene patterns, bodily movements etc. Psychological positivists will also look at biological observables but will add behavioural factors, child rearing practices and brain abnormalities that cause identifiable behaviour outcomes.
Many modern scientists have virtually discredited positivism in favour of what we call the hypothetico-deductionist approach or a falsficationist approach. This approach begins with theoretical conjectures (or hypotheses) and then seeks to prove or disprove them by means of empirical evidence. However, whatever the differences in method both positivism and hypothetico-deductionism seek empirical evidence for their theoretical positions. Implicit in these approaches is the idea that the scientist is an objective disinterested observer of natural events with no preconceptions about them.
In the case of physics these natural events or laws are said to be found in nature itself as, for example, in the study of such phenomena as the movement of the planets around the Sun, the effect of gravity on the tides and the phenomenon of the seasons created by the movement of the Earth around the Sun. In these cases the object of study is seen as governed by universal natural laws which the scientist has to discover. When this approach is applied in the human or social sciences we have to understand our object of study (i. e. human beings or societies) as also governed or regulated by rules that the scientist has to discover.
Thus Biological Criminologists will use data from such sources as twin studies, family studies, genetic patterns, biochemical aspects and so on anything that can be studied by means of objective, methods and which may throw up some biological explanation of that behaviour or a principle or a law that explains that behaviour. It follows that in positivist criminality, criminals are identified as certain kinds Of human beings who are governed by events or natural phenomena that have been set in place by something external to them and, in a sense, beyond their control.
Thus criminals do not make decisions about their criminal behaviour they are, as it were, caused to behave in this way by factors that operate in a sense, behind their backs. Thus, so-called abstract views of human nature such as that they are rational and use reason in making choices about their actions have to be discarded as a cause of behaviour in favour of non-rational causes such as determination by such things as biological inheritance or forms of social conditioning or, in many cases, a combination of both (as in Eysenck).
Positivists aim is to identify those with criminal tendencies or those already classified as criminals and use them as their data base. Their goal is to ascertain what has caused their criminality and then to look for ways of correcting such criminality or, even better, to ascertain those with tendencies for criminality (before hopefully they commit a crime) and to put some preventative measures in place. Biological positivists generally look for biological causes generally in genetic inheritance. A well know example is that of Klinenfelters Syndrome where a study of known criminals identified was said to be an extra y chromosome.