In 1890, William James defined psychology as "the science of mental life, both of its phenomena and their conditions ''. This definition enjoyed widespread currency for decades. However, this meaning was contested, notably by radical behaviorists such as John B. Watson, who in his 1913 manifesto defined the discipline of psychology as the acquisition of information useful to the control of behavior. Also since James defined it, the term more strongly connotes techniques of scientific experimentation. Folk psychology refers to the understanding of ordinary people, as contrasted with that of psychology professionals.
who said psychology is the science of mental life
William James