Without question, there are unfinished tasks still lying in this field. What we have hitherto set forth needs to be rounded out in many ways by working out fully the existential a priori of philosophical anthropology and taking a look at it. But this is not the aim of our investigation. Its aim is one of fundamental ontology . Consequently, if we inquire about Being-in as our theme, we cannot indeed consent to nullify the primordial character of this phenomenon by deriving it from others—that is to say, by an inappropriate analysis, in the sense of a dissolving or breaking up. But the fact that something primordial is underivable does not rule out the possibility that a multiplicity of characteristics of Being may be constitutive for it. If these show themselves, then existentially they are equiprimordial. The phenomenon of the equiprimordiality of constitutive items has often been disregarded in ontology, because of a methodologically unrestrained tendency to derive everything and anything from some simple 'primal ground'.

[132] In which direction must we look, if we are to characterize Being-in, as such, phenomenally? We get the answer to this question by recalling what we were charged with keeping phenomenologically in view when we called attention to this phenomenon: Being-in is distinct from the present-at-hand insideness of something present-at-hand 'in' something else that is present-at-hand; Being-in is not a characteristic that is effected, or even just elicited, in a present-at-hand subject by the 'world's' Being-present-at-hand; Being-in is rather an essential kind of Being of this entity itself. But in that case, what else is presented with this phenomenon than the commercium which is present-at-hand between a subject present-at-hand and an Object present-at-hand? Such an interpretation would come closer to the phenomenal content if we were to say that Dasein is the Being of this 'between'. Yet to take our orientation from this 'between' would still be misleading. For with such an orientation we would also be covertly assuming the entities between which this "between", as such, 'is', and we would be doing so in a way which is ontologically vague. The "between" is already conceived as the result of the convenientia of two things that are present-at-hand. But to assume these beforehand always splits the phenomenon asunder, and there is no prospect of putting it together again from the fragments. Not only do we lack the 'cement'; even the 'schema' in accordance with which this joining-together is to be accomplished, has been split asunder, or never as yet unveiled. What is decisive for ontology is to prevent the splitting of the phenomenon—in other words, to hold its positive phenomenal content secure. To say that for this we need far-reaching and detailed study, is simply to express the fact that something which was ontically self-evident in the traditional way of treating the