Gustav Fechner
Fechner, along with Wilhelm Wundt and Hermann von Helmholtz, is recognized as one of the founders of modern experimental psychology. His clearest contribution was the demonstration that because the mind was susceptible to measurement and mathematical treatment, psychology had the potential to become a quantified science. Theorists such as Immanuel Kant had long stated that this was impossible, and that therefore, a science of psychology was also impossible.
Daniel Levinson
Daniel J. Levinson (May 28, 1920 – April 12, 1994), a psychologist, was one of the founders of the field of positive adult development. Levinson is most well known for his theory of stage-crisis view, however he also made major contributions to the fields of behavioral, social, and developmental psychology. His interest in the social sciences began with studies on personality and authoritarianism, and eventually progressed to studies on development. Greatly influenced by the work of Erik Erikson, Elliott Jaques, and Bernice Neugarten, his stage-crisis view sought to incorporate all aspects of adult development in order to establish a more holistic approach to understanding the life cycle. In doing so, Levinson discussed the various developmental tasks and/or crises that one must address within each stage as well as how they contribute to the progression of development. Although much controversy surrounds his research methods, Levinson interviewed both men and women to uncover concrete patterns that occur within similar age ranges. Through these studies, he determined that men and women essentially progress through the same cycle of life, however they differentiate in what he refers to as "The Dream". He published his findings and theory within his two major books, "The Seasons of a Man's Life" and "The Seasons of a Woman's Life"; both of which remain as influential publications within the field of psychology. Being both simple in nature and open to further investigation, Daniel Levinson's legacy and lasting contributions are mainly to theory and entail profound implications for social as well as behavioral psychology.