Now, how did the beginning of such a self-examination come about? A beginning was impossible so long as sensualism, or better, a psychology of data, a tabula rasa psychology, held the field. Only when Brentano promoted psychology to being a science of vital intentional experiences was an impulse given that could lead further – though Brentano himself had not yet overcome objectivism and psychological naturalism*. The development of a real method of grasping the fundamental essence of spirit in its intentionalities and consequently of instituting an analysis of spirit with a consistency reaching to the infinite, led to transcendental phenomenology. It was this that overcame naturalistic objectivism, and for that matter any form of objectivism, in the only possible way, by beginning one’s philosophizing from one’s own ego; and that purely as the author of all one accepts, becoming in this regard a purely theoretical spectator. This attitude brings about the successful institution of an absolutely autonomous science of spirit in the form of a consistent understanding of self and of the world as a spiritual accomplishment. Spirit is not looked upon here as part of nature or parallel to it; rather nature belongs to the sphere of spirit. Then, too, the ego is no longer an isolated thing alongside other such things in a pregiven world. The serious problem of personal egos external to or alongside of each other comes to an end in favor of an intimate relation of beings in each other and for each other.
note *: For his part, Brentano complained that his theory of intentionality had been transformed by Husserl into an a priori idealism.
EDMUND HUSSERL: Philosophy and the Crisis of European Man