Psychology can be defined as the science of activities of the individual. The science of human behavior is actually a group of sciences. On one side we find the physiology investigating the organs and cells that do the work of the organism and on the other hand we see the social sciences studying the nations and the groups of mankind. There is a room for a middle science that shall focus its attention on the individual. This middle science is called psychology. Psychology studies the individual’s activities through out his span of life, from his small beginnings before birth up through infancy, childhood, and adolescence to maturity, and still further on through the declining years. During this life history he remains the same individual, but his behavior shows continuity along with many changes. Psychology compares child and the adult, the normal and the abnormal, the human and the animal. It is interested in the differences between one individual and another, and still more interested, if possible, in the general laws of activity holding good even of very different individuals – laws, for example growth, learning, thinking and emotion.
As per above statement, the word ‘activity’ is used here in a very broad sense. [linkunit]It includes not only the motor activities like walking, talking, but also cognitive activities like seeing, hearing, remembering, thinking and emotional activities like laughing, crying, feeling happy or sad etc. These last, and it may seem passive yet they are activities, for they depend on the life of the organism. Any manifestation in life can be called as activity.