Working in this field I felt that I had begun a task methodologically and technically sound and necessary, the broader elaboration of which could not be expected for decades. Nevertheless it soon became clear that though these problems are difficult, they are by no means impossible to solve. One had only to clear out a number of hoary philosophical prejudices and to set his scientific goal high enough to arrive at explanation and prediction. Today it can no longer be doubted that the questions set, for example, by psychoanalysis are readily accessible to experimental clarification if only appropriate methods and concepts are employed.

p. v-vi. - A Dynamic Theory of Personality, 1935