artificially into separate successive forward movements. Your impression that these conceptions require further elucidation is correct, but the attempt would lead us too far afield. We will, however, decide at this point to call this _arrest_ in a component-impulse at an early stage a FIXATION (of the impulse). The second danger in a development by stages such as this we call REGRESSION; it also happens that those portions which have proceeded further may easily revert in a backward direction to these earlier stages. The impulse will find occasion to _regress_ in this way when the exercise of its function in a later and more developed form meets with powerful external obstacles, which thus prevent it from attaining the goal of satisfaction. It is a short step to assume that fixation and regression are not independent of each other; the stronger the fixations in the path of development the more easily will the function yield before the external obstacles, by regressing on to those fixations; that is, the less capable of resistance against the external difficulties in its path will the developed function be. If you think of a migrating people who have left large numbers at the stopping-places on their way, you will see that the foremost will naturally fall back upon these positions when they are defeated or when they meet with an enemy too strong for them. And again, the more of their number they leave behind in their progress, the sooner will they be in danger of defeat. It is important for comprehension of the neuroses that you should keep in mind this relation between fixation and regression. You will thus acquire a secure foothold from which to investigate the causation of the neuroses—their ætiology—which we shall soon consider.