No logically successful clarification of the concept of insight exists in psycho-analytic theory which will (1) differentiate between the various uses of the term, and (2) relate these uses theoretically to therapeutic aims. Current definitions of the various types of insight are linguistically confused. The author attempts a clarification by applying Bertrand Russell's concepts of knowledge by description and knowledge by acquaintance in order to be able to define insights according to the manner in which they were achieved. Both methods are necessary for successful treatment.