When we bring to mind concretely what has been exhibited in the interpretation of “phenomenon” and “logos” we are struck by an inner relation between what is meant by these terms. The expression “phenomenology” can be formulated in Greek as legein ta phainomena. But legein means apophainesthai. Hence phenomenology means: apophainesthai ta phainomena — to let what shows itself be seen from itself, just as it shows itself from itself. That is the formal meaning of the type of research that calls itself “phenomenology.” But this expresses nothing other than the maxim formulated above: “To the things themselves!”
Accordingly, the term “phenomenology” differs in meaning from such expressions as “theology” and the like. Such titles designate the objects of the respective disciplines in terms of their content. “Phenomenology” neither designates the object of its researches nor is it a title that describes their content. The word only tells us something about the how of the demonstration and treatment of what this discipline considers. Science “of’ the phenomena means that it grasps its objects in such a way that everything about them to be discussed must be directly indicated and directly demonstrated. The basically tautological expression “descriptive phenomenology” has the same sense. Here description does not mean a procedure like that of, say, botanical morphology. The term rather has the sense of a prohibition, insisting that we avoid all nondemonstrative determinations. The character of description itself, the specific sense of the logos, can be established only from the “material content” [” Sachheit”] of what is “described,” that is, of what is to be brought to scientific determinateness in the way phenomena are encountered. The meaning of the formal and common concepts of the phenomenon formally justifies our calling every way of indicating beings as they show themselves in themselves “phenomenology.”
Now what must be taken into account if the formal concept of phenomenon is to be deformalized to the phenomenological one, and how does this differ from the common concept? What is it that phenomenology is to “let be seen”? What is it that is to be called “phenomenon” in a distinctive sense? What is it that by its very essence becomes the necessary theme when we indicate something explicitly? Manifestly it is something that does not show itself initially and for the most part, something that is concealed, in contrast to what initially and for the most part does show itself. But at the same time it is something that essentially belongs to what initially and for the most part shows itself, indeed in such a way that it constitutes its meaning and ground.*
But what remains concealed in an exceptional sense, or what falls back and is covered up again, or shows itself only in a distorted way, is not this or that being but rather, as we have shown in our foregoing observations, the Being of beings. It can be covered up to such a degree that it is forgotten and the question about it and its meaning altogether omitted. Thus what demands to become a phenomenon in a distinctive sense, in terms of its most proper content, phenomenology has taken into its “grasp” thematically as its object.
From Being and Time – Heidegger