Commentary on Cronbach’s ‘The Two Disciplines of Scientific Psychology’ In this paper Lee Cronbach delivers his visionary presidential address to the American Psychological Association (APA), calling for the unification of experimental and correlational psychology in which he argued that psychology continues to this day to be limited by the dedication of its investigators to one or the other method of inquiry rather than to scientific psychology as a whole. He discusses the two streams on branches of psychology that have run through the last century.One stream being the experimental and the other correlational psychology. He describes the essential features of each approach to asking questions about human nature and he strongly hints at the benefits to be gained by unification. Put simply, Cronbach sees this as a puppet show where the experimentalist manipulates the puppets to arrive at a successful outcome while the correlationist watches the interaction of the puppets as he would people, to see how environment, social elements and the like affects them.Cronbach is proposing a coming together of these two strands of psychology to compliment each other and arrive at a more complete solution. The experimenter is more concerned with situations that he can closely control i. e. experiments with laboratory animals in a closely confined situation where he can introduce variables and see how his subjects react to stimuli and measure the responses. The correlationist is more interested in looking at the wider picture and observing how subjects interact with each other and with their environment, social surroundings and other subjects etc.Experimental methods are the only ones that can produce a definite result as it calculates correlations between variables specifically those manipulated and those affected by the manipulation, therefore it can conclusively demonstrate causal relations between variables. Alternatively, in correlational research, variables are not influenced, but researchers only measure them and look for relations (correlations) between some set of variables. While correlational studies can suggest that there is a relationship between two variables, they cannot prove that one variable causes a change in another variable.In other words, correlation does not equal causation. However, experimental data may potentially provide qualitatively better information as only experimental data can conclusively demonstrate causal relations between variables. Cronbach tells us that experimental and correlational psychology are two disciplines that characterise the field of scientific psychology. According to him, the job of science is to ask questions of nature, and that a discipline is a method of asking questions and testing answers to determine whether they are sound.He notes that correlational psychologists are interested in the already existing variations between individuals, social groups and species. They measure how these variations relate to performance in other domains. It is the job of the correlator to observe and organise data from nature’s experiments. The two disciplines have very little influence over the other. Facts from correlational research do not generalise to experimental research or vice versa. Cronbach states that the main difference between the two is that correlational psychologists actually like people.Experimental psychologists are interested in controlling situational variables to permit rigorous tests of hypotheses and confident statements about causation. The experimental psychologist is concerned with how different treatments result in the greatest average effects for individuals or groups of individuals. Emphasis is placed on controlling for situational variations across treatment conditions in order to make valid comparisons of treatment effects. What the experimental psychologist views as error and tries to prevent from confusing the experimental effects, is the aim of study for the correlational psychologist.According to Cronbach, the two streams differ in their philosophical underpinnings, methods of inquiry, topical interests and the loci of application. However, he also conceptualized the two strains broadly to include the research designs, measures and statistical analyses a researcher uses. Cronbach proposes a merger of the two disciplines when he suggests aptitude treatment interaction. He argues that psychologists should consider how aptitudes might interact with certain aspects of treatment to attenuate effects.The idea was that treatments should be designed to fit individuals or groups of individuals with certain aptitudes or aptitude patterns. The two disciplines, if kept independent, can only give wrong answers or no answers at all regarding certain important problems. Both streams of psychology are important in developing outcomes or solutions in certain situations but Cronbach suggests a coming together of the two strains in order to produce a more definite single branch of psychology in the way that the physical sciences i. e. chemistry and physics have become.It is vital to understand that each procedure has got its share of importance, given that psychology depends more on empirical methods for its varied and unrelated studies. Therefore, it is important to understand that each and every given research demands a specific procedural method, hence, the two cannot cover each and every sphere of psychology but they provide a concise destiny in determining specific attitudes or behavioural changes. Cronbach believes that the conflicting principles of the correlationist and the experimentalists can be combined into a new and integrated applied psychology.The two disciplines are in active conflict and unless they can agree on their efforts, they can hold each other to a standstill. The field of psychology would be improved if experimentalists and correlationalists could share methods, theories, and findings. The job of applied psychology is to improve decisions about people. The greatest social benefit will come from applied psychology if we can find for each individual the treatment to which he can most easily adapt. This calls for the joint application of experimental and correlational psychology. .