something like being becomes at all intelligible. We interpret being by way of time (tempus). The interpretation is a Temporal one.* The fundamental subject of research in ontology, as determination of the meaning of being by way of time, is Temporality.
We said that ontology is the science of being. But being is always the being of a being. Being is essentially different from a being, from beings. How is the distinction between being and beings to be grasped? How can its possibility be explained? If being is not itself a being, how then does it nevertheless belong to beings, since, after all, beings and only beings are? What does it mean to say that being belongs to beings? The correct answer to this question is the basic presupposition needed to set about the problems of ontology regarded as the science of being. We must be able to bring out clearly the difference between being and beings in order to make something like being the theme of inquiry. This distinction is not arbitrary; rather, it is the one by which the theme of ontology and thus of philosophy itself is first of all attained. It is a distinction which is first and foremost constitutive for ontology. We call it the ontological difference—the differentiation between being and beings. Only by making this distinction—krinein in Greek—not between one being and another being but between being and beings do we first enter the field of philosophical research. Only by taking this critical stance do we keep our own standing inside the field of philosophy. Therefore, in distinction from the sciences of the things that are, of beings, ontology, or philosophy in general, is the critical science, or the science of the inverted world. With this distinction between being and beings and the selection of being as theme we depart in principle from the domain of beings. We surmount it, transcend it. We can also call the science of being, as critical science, transcendental science. In doing so we are not simply taking over unaltered the concept of the transcendental in Kant, although we are indeed adopting its original sense and its true tendency, perhaps still concealed from Kant. We are surmounting beings in order to reach being. Once having made the ascent we shall not again descend to a being, which, say, might lie like another world behind the familiar beings. The transcendental science of being has nothing to do with popular metaphysics, which deals with some being behind the known beings; rather, the scientific concept of metaphysics is identical with the concept of philosophy in general—critically transcendental science of being, ontology. It is easily seen that the ontological difference can be cleared up and carried out unambiguously for ontological inquiry only if and when the meaning of being in general has been explicitly brought to light, that is to say, only
* In its role as condition of possibility of the understanding of being, temporality is Temporality. See Lexicon: Temporality.