Time Juan José Sanguineti I. Nature’s time. 1. The Notion of Time. 2. Present, Past and Future. Simultaneity and Unity of Time. 3. Continuous and Discrete Character of Time. 4. Directionality of Time. 5. Ontology of Time. - II. Some Philosophical Aspects of Time Related to the Natural Sciences. 1. The Scientific Approach to Time. 2. Absolute and Relative Time. 3. The Sequential Order of Time and Causality. 4. The Arrow of Time. 5. Temporality and A-temporality. 6. The Beginning and the End of Time. - III. Time in Human Life - IV. The Nature of Time according to Christian Revelation. I. Nature’s Time 1. The Notion of Time. We experience time as a continuous and unstoppable passage from what has been to what is now and, further, to what will be. This almost imperceptible flow does not mean that time is an absolute entity (the so-called theory of “absolute” or empty time, advanced by Newton, among others); indeed, in reality, time is a characteristic that derives from movement (“relational theory” of time, differently formulated by Aristotle and Leibniz) (cf. Le Poidevin, 1993). Every change contains an irreducible element of sequence from a “before” to an “after”, and this is temporality in its original moment, prior to any measurement (we should not, however, place the prius and posterius in an empty time). Wherever there is a sequence, there is a form of temporality. From this point of view, any subsequent phenomenon produces its own time; yet, because of the connections among natural beings, we usually determine the before and after of many phenomena relatively to certain standard sequences (for example, we work before or after sunset). Time, therefore, is the sequential order of before/after among events that arises from movement (cf. Aristotle, Physics, book IV). Things that change, however, remain the same in many other respects; in a more common sense, then, time is the “duration of changeable beings,” a duration that is always immersed in change, given that all natural beings undergo constant internal changes and also vary because of the continuing mutations of surrounding nature. Hence, a given entity lasts for an hour, a day, a few years, as it