The article “On Small Differences in Sensation”¯ by C.S. Peirce and J. Jastrow (1885) and “The Two Disciplines of Scientific Psychology”¯ by L.J. Cronbach reveal the evolution of psychology and the development of psychology as a science in the course of about the half of a century.
In fact, the article reveals a consistent progress of psychology from the first experiments in the field of psychology and the first attempts to view psychology from the functional point of view made by Peirce and Jastrow to the development of scientifically grounded theories which became mainstream movements in psychology.
To put it more precisely, Perice and Jastrow focused on sensation analysis that was one of the first manifestation of functional psychologist study. The researchers revealed the existence of differences between sensations. In such a way, they revealed existing psychological differences between individuals and the impact of external factors on them. Cronbach conducted a more fundamental research in regard to functional psychology. In fact, unlike his predecessors, Cronbach views functional psychology as one of two major disciplines of scientific psychology. In such a way, functional psychology became not a mere experiment as was the case of the study conducted by Peirce and Jastrow, but it was a scientific discipline on the ground of which psychological theories could be developed.
These articles reveal the tremendous progress of psychology as a science within about seventy years period. These articles help to understand the changes that took place in psychology and the change of view of specialists on psychology as a science. Obviously, the study of Peirce and Jastrow were grounded on their enthusiasm, whereas Cronbach conducts a research that bears significant scientific values but, in actuality, it continues studies started by his predecessors in the late 19th century.