A.C. Grayling states that metaphysics is the branch of philosophy concerned with the nature of reality. One set of metaphysical questions involves issues of time and causality (Grayling 183). These are not new topics by any means and have been asked since the beginning of philosophy, and while we may believe we have a clear idea of time and its components, a close analysis shows that we do not.
One of the key issues in Greek philosophy concerned the matter of change and its opposite, permanence, and many of the earliest philosophical arguments centered on matters of change, motion, and their relationship to the passage of time. In considering another issue, the question of what the basic stuff of the universe might be, the stuff from which all else is composed, the ancient Greeks wanted to answer this question so as to solve the problems of apparent stability and actual change, also related to the passage of time during which that which is stable seems to change and become something else. Heraclitus stated that it was not possible to step into the same river twice, thus indicating his belief in the prevalence of change all around. Aristotle continues the discussion of change and permanence and their relationship to time in the passages under discussion from his Physics and expresses a number of concepts and conclusions regarding time and change in the world. Heraclitus believed that stability was an illusion. Parmenides thought that motion was an illusion. Plato offered a compromise in his view of a dual world, one unstable and transient and the other permanent and unchanging. Aristotle abandoned Plato's dualism and believed there was only one world, observable and comprehensible, and made up of a plurality of substances.
Aristotle considers the question of time beginning in Chapter 10 of his Physics. Time is described by Aristotle as a unity, a oneness, a singularity, just is there is one world:
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