Dasein, the possibilities and destinies of philosophy are bound up with man's existence, and thus with temporality and with historicality, and indeed in a more original sense than with any other science. Consequently, in clarifying the scientific character of ontology, the first task is the demonstration of its ontical foundation and the characterization of this foundation itself.
The second task consists in distinguishing the mode of knowing operative in ontology as science of being, and this requires us to work out the methodological structures of ontological-transcendental differentiation. In early antiquity it was already seen that being and its attributes in a certain way underlie beings and precede them and so are a proteron, an earlier. The term denoting this character by which being precedes beings is the expression a priori, apriority, being earlier. As a priori, being is earlier than beings. The meaning of this a priori, the sense of the earlier and its possibility, has never been cleared up. The question has not even once been raised as to why the determinations of being and being itself must have this character of priority and how such priority is possible.To be earlier is a determination of time, but it does not pertain to the temporal order of the time that we measure by the clock; rather, it is an earlier that belongs to the "inverted world." Therefore, this earlier which characterizes being is taken by the popular understanding to be the later. Only the interpretation of being by way of temporality can make clear why and how this feature of being earlier, apriority, goes together with being. The a priori character of being and of all the structures of being accordingly calls for a specific kind of approach and way of apprehending being— a priori cognition.
The basic components of a priori cognition constitute what we call phenomenology. Phenomenology is the name for the method of ontology, that is, of scientific philosophy. Rightly conceived, phenomenology is the concept of a method. It is therefore precluded from the start that phenomenology should pronounce any theses about being which have specific content, thus adopting a so-called standpoint.
We shall not enter into detail concerning which ideas about phenomenology are current today, instigated in part by phenomenology itself. We shall touch briefly on just one example. It has been said that my work is Catholic phenomenology—presumably because it is my conviction that thinkers like Thomas Aquinas and Duns Scotus also understood something of philosophy, perhaps more than the moderns. But the concept of a Catholic phenomenology is even more absurd than the concept of a Protestant mathematics. Philosophy as science of being is fundamentally distinct in method from any other science. The distinction in method between, say, mathematics and classical philology is not as great as the difference between mathematics and philosophy or between philology and philosophy. The