Second, that entity which in every case has Being-in-the-world as the way in which it is. Here we are seeking that which one inquires into when one asks the question 'Who?' By a phenomenological demonstration1 we shall determine who is in the mode of Dasein's average everydayness. (See the fourth chapter of this Division.)
Third, Being-in [In-sein] as such. We must set forth the ontological Constitution of inhood [Inheit] itself. (See the fifth chapter of this Division.) Emphasis upon any one of these constitutive items signifies that the others are emphasized along with it; this means that in any such case the whole phenomenon gets seen. Of course Being-in-the-world is a state of Dasein2 which is necessary a priori, but it is far from sufficient for completely determining Dasein's Being. Before making these three phenomena the themes for special analyses, we shall attempt by way of orientation to characterize the third of these factors.
What is meant by "Being-in"? Our proximal reaction is to round out this expression to "Being-in 'in the world'", and we are inclined to understand this Being-in as 'Being in something' ["Sein in . . ."]. This [54] latter term designates the kind of Being which an entity has when it is 'in' another one, as the water is 'in' the glass, or the garment is 'in' the cupboard. By this 'in' we mean the relationship of Being which two entities extended 'in' space have to each other with regard to their location in that space. Both water and glass, garment and cupboard, are 'in' space and 'at' a location, and both in the same way. This relationship of Being can be expanded: for instance, the bench is in the lecture-room, the lecture-room is in the university, the university is in the city, and so on, until we can say that the bench is 'in world-space'. All entities whose Being 'in' one another can thus be described have the same kind of Being—that of Being-present-at-hand—as Things occurring 'within' the world. Being-present-at-hand 'in' something which is likewise present-at-hand, and Being-present-at-hand-along-with [Mitvorhandensein] in the sense of a definite location-relationship with something else which has the same kind of Being, are ontological characteristics which we call "categorial": they are of such a sort as to belong to entities whose kind of Being is not of the character of Dasein.
Being-in, on the other hand, is a state of Dasein's Being; it is an existentiale. So one cannot think of it as the Being-present-at-hand of some corporeal Thing (such as a human body) 'in' an entity which is present-at-hand. Nor does the term "Being-in" mean a spatial 'in-one-another-ness' of things present-at-hand, any more than the word 'in' primordially signifies a spatial relationship of this kind.i
1 Here we follow the older editions in reading, 'Ausweisung'. The newer editions have 'Aufweisung' ('exhibition').
2 '... Verfassung des Daseins ...' The earliest editions read 'Wesens' instead 'Daseins'. Correction is made in a list of errata.