There are several theories on the study in criminology. Among those theories, the Pure-Classical Theory of Criminology and the Neo-Classical Theory of Criminology are two major schools in criminological studies. These two schools of criminology try to explain the crime causation and the methods adopted to control them in their rationalization. This study focuses to discuss the historical evolution of the pure-classical and neo-classical approaches and their applicability on criminology into the modern criminal justice system with a special review on selected general defences of substantial criminal law in Sri Lanka.