Phenomenology and Existentialism
The invention of the term “phenomenology” is generally attributed to Jean-Henri Lambert, who thus names in the fourth part of his New Organon (1764) the “doctrine of appearance”
A section of Kant’s Critique of Pure Reason was to be called Phenomenology, but Kant eventually replaced this name with Transcendental Aesthetics. Kant fathered the distinction between the "thing in itself" and the phenomenon (what shows itself), the latter being given in the transcendental framework of space, time and causality. Kant’s thesis is that there is only an a priori framework in which objects can "encounter" us.and which allows their representation. This framework, which is none other than the structure of our knowledge, will open up the possibility of universal knowledge.
Johann Gottlieb Fichtea
Phenomenology is a central concept in the philosophy of Johann Gottlieb Fichte. It designates the part of the doctrine of science which develops the phenomenalization (appearance, exteriorization) of the foundation and principle of knowledge. There can only be absolute knowledge (which is not knowledge of an object but of what makes knowledge effectively knowledge) phenomenalized. Also, Fichte opposes the doctrine of phenomenon or phenomenology to the doctrine of being and truth. In his late thought, Fichte even identifies phenomenology with the doctrine of science, because without it, “absolute knowledge” would not exist.
From the Kantian theses, Hegel deduces that with the phenomenon, consciousness discovers the structure of its own knowledge, thus rising to self-consciousness. In the Phenomenology of Spirit Hegel traces the course of this consciousness in the history of its manifestations, of its figures, which are so many self-experiences in its drive towards science..
Arthur Schopenhauer claimed that the world is our representation (that is to say that being and being a representation, for the subject, are all one), for him it is always a question of seeking deeper than this first evidence: how to know what the world can be in its being in itself? It is for him to seek the essence of the phenomenon from a preliminary descriptive study of the given phenomenal and in particular, of the way in which my own body is given to me as "will".
See also: What is Phenomenology – an Introduction