The Group Mind: A Sketch of the Principles of Collective Psychology

"Until the later decades of the nineteenth century, psychology continued to concern itself almost exclusively with the mind of man conceived in an abstract fashion, not as the mind of any particular individual, but as the mind of a representative individual considered in abstraction from his social settings as something given to our contemplation fully formed and complete..."
William McDougall was an early 20th century psychologist who wrote a number of highly influential textbooks, and was particularly important in the development of the theory of instinct and of social psychology in the English-speaking world. He was an opponent of behaviourism and stands somewhat outside the mainstream of the development of Anglo-American psychological thought in the first half of the 20th century; but his work was very well known and respected among lay people.