Behavioural theories were the main tool of psychologists from the 1960s to the 1980s. These theories attempt to use a person's past and the environment she grew up in as the factors to describe and predict behaviour. The basic premise of behavioural theories is that human nature is completely reliant on the environment. Modern psychologies have since abandoned behavioural theories for the most part, because these theories are severely limited.
Ignorance of Genetics
Behavioural theories completely reject the idea of genetics having an influence on human behaviour. Psychology in its modern form, on the other hand, accepts genetic influence on human behaviour as a fact. One of the most prominent social psychologists, Kurt Lewin, tried to resolve the limitation of behavioural theories by giving his famous equation: behaviour is a function of the person (genetic nature) and the environment. Behavioural theories lack one of the vital factors in Lewin's equation, and cannot completely describe human behaviour.
Psychologists that developed behavioural theories backed these theories on experiments containing stimuli that are not easily relatable. In these experiments artificial environments are constructed to condition subjects to associating these normally unrelatable stimuli, such as food and electric shock. The psychologists then generalised their results to all sets of stimuli, no matter how easily the relationships between these stimuli are made. The limitation in this case is that such a generalisation cannot scientifically follow such experiments. In short, this generalisation by behavioural theories is flawed.
Behavioural theories also ignore the cognitive aspects of human psychology. Because behavioural theories explain everything in terms of the "outside" (behaviour) and discard the "inside" (mental processes, genetic influences, emotions and so on), ideas like memory and though processes cannot enter the behavioural explanations of human actions. However, much research in psychometrics, the field of psychological measurement, has shown that these mental aspects predict much of human behaviour. One example is how personality tests correlate to human decisions such as job and mate selection. In this respect, behavioural theories see humans as no different creatures than animals: mental processes are not important.
Behavioural theories are useless in explaining mental problems. Because behavioural theories treat the human mind as a "black box," they have no place in explaining diseases that are associated with abnormal thought processes such as schizophrenia and paedophilia. It then follows that behavioural theories cannot assist those with mental diseases in their treatment processes.