"We wish to exhibit history and nature so that we may regard them before scientific elaboration, so that we may see both realities in their reality. This means that we wish to arrive at a horizon from which history and nature can be originally contrasted. This horizon must must itself be a field of constituents against which history and nature stand out in relief. Laying out this field is the task of the "prolegomena to a phenomenology of history and nature." We shall approach this task... by way of a history of the concept of time. ...both historical reality and natural reality are continuities that run their course in time... In natural science, especially in its basic science of physics, the measurement of time plays a fundamental role in defining its objects. The investigation of historical reality is completely incomprehensible without a chronology, an ordination of time. Viewed simply from the outside, history and nature are temporal. To the totality of temporal reality we tend to juxtapose the extratemporal constituents which, for example, are the topic of research in mathematics. In addition... we are familiar with supratemporal constituents in metaphysics or theology, understood as eternity. In a very schematic and crude way, time already announces itself as one 'index' for the differentiation and delimitation of domains of being as such. The concept of time discloses particulars about type and reality for such a demarcation of the universal realm of entities. It becomes, according to the particular stage of its development as a concept, a guide for the question of the being of entities and their potential regions. This occurs without an expressly fundamental consciousness of such a role, which is thus fulfilled in a correspondingly crude way, without bringing to the fore the possibilities which are implied in such an orientation. The concept of time is therefore... linked to the basic question of philosophy, if indeed this asks about the being of entities, the actuality of the actual, the reality of the real."