Dr Saugstad’s dominant interest was in the area of thinking. Many psychologists would have been familiar with his published work in this field at the time. To gain a clearer understanding of the thought processes, he carried out extensive studies of perception.First published in 1965, this book originated in an attempt to reconcile a phenomenological and a behavioristic approach to psychology. Basic assumptions in phenomenology, behavioristics and psychophysics are examined. It is shown that in phenomenology theoretical concepts tend to be treated as observations, whereas in behavioristics observations tend to be treated as theoretical concepts. It is pointed out that the relationship between observer and observed event is confused throughout the history of psychology. This confusion, the author insists, is due to the fact that man’s cognitive processes are to a large extent unknown. In relating observations to each other, the psychologist will of necessity contaminate his observations unless he follows specific rules. This fundamental point had apparently not been previously realized by psychologists.In order to develop an adequate conception of scientific psychology, the nature of man’s cognitive processes must be taken into account. When this is done, one sees that drastic revisions of current conceptions of psychology are necessary. This book presents a conception of psychology which does take into account man’s cognitive processes.