In this article, I analyze the working principle and associated concepts of the method of eidetic variation as illustrated by Husserl in Experience and Judgment. In so doing, I scrutinize the very specific sense in which, for Husserl, variation must be free in order to have intuition of a universal as pure, that is, as having a priori validity. I then discuss Husserl’s problematic claim that, even if totally free, the eidetic variation is actually not sufficient to achieve purity. The reason for its insufficiency, I argue, must be sought in the habits of phantasy. To this aim, I first undertake a phenomenological analysis of the essence of these habits as passive tendencies of the phantasizing ego. Then, I show that they hinder the intuition of the universal as pure by contaminating the purity of the free possibilities to be varied. Finally, I discuss whether habits of phantasy can be put out of play and whether, depending on the realizability of such a task, the whole method of eidetic variation, and, in relation to it, the possibility of a priori knowledge advocated by Husserl is to be put into question.