Since the very beginning of the human history and up to the present times, the question of time has been a matter of the major philosophical and mathematical concern. Where scientists sought to establish the single and universal definition of time as applied to astronomical and geometrical linear concepts, philosophers tried to reconsider the relevance of time through the prism of its relativity, instability, and its relation to eternity. Given the continuous evasiveness of time and its never-stopping nature, it is difficult to deny that the concept of time comprises numerous features that are not always readily visible to researchers. Simultaneously, our growing dependence on time turns the latter into the critical component of our daily functioning. In reality, and taking into account numerous ideas about time, time is an intangible category which in our world is directly associated with the movement of space bodies around the earth, and which also exemplifies a relative measure of events.Really, the whole history of mankind is associated with the continuous search for the single and universal definition of time. For years and centuries hundreds of scientists, archeologists, anthropologists, philosophers, and religious adherents sought to create a clearer vision of time. In the light of its evasiveness, and given the intangible nature of time, it was more and more difficult for humans to come to a simple and common agreement with regard to the definition of time. Now, as we find ourselves more and more dependent on time, we also find it more and more difficult to determine, what it is that we see through the clocks, alarms, and calendars. It would be fair to say that “time is represented through change, such as the circular motion of the moon around the earth. The passing of time is indeed closely connected to the concept of space” (Science Daily), but is it enough to say that time is nothing more but the motion of celestial bodies around the earth?Certainly, the concept of time extends far beyond the boundaries of space consciousness, and while individuals try to determine what time is, a whole set of considerations and criteria needs to be taken into account. Historical and philosophic wisdom may help clarify the major time controversies. To begin with, it is in the dialogue between Plato and Timaeus that we first encounter the growing ancient interest toward time. “He thought of making a certain movable image of eternity, and, at once with ordering heaven, he made an eternal image going according to number, that which we have named Time” (Reichenbach 43). Here, the definition of time comprises both physical and metaphysical understanding of continuous motion, and also confirms the cosmological nature of time on our planet. For Plato, the concept of time is nothing else but a unique combination of eternity and change. This uniqueness is justified by the growing confidence that time, on the one hand, exemplifies stability and a measure of everything, and on the other hand, works as a never-stopping evasive machine. Nevertheless, it is with Plato that scientists and philosophers have gradually come to realize the importance and role of space bodies in designing the vision of time and its relativity. It is with Plato that we view space bodies as the major divisions of circular time. Space bodies link the concept of time to the concept of motion. Through the dialogue between Plato and Timaeus we see stars and other planets as indicators of intangible time; ultimately, it is space that is associated both with eternity and continuous motion. Does that mean that time is a purely philosophical concept and has nothing to do with specific mathematical sciences?In reality, scientists in general, and physicists in particular truly believe that they can scientifically justify and ground the concept of time. Although the scientific side of time is still unclear, it is obvious that researchers and scholars in science will further use their mathematical and mechanical knowledge to develop new time theories. Einstein is well-known for his works about relativity and time, but before Einstein, Galileo and Isaac Barrow also tried to produce a single definition of time. For Barrow, “time denotes not an actual existence but a certain capacity or possibility for a continuity of existence; just as space denotes a capacity for intervening length. Time does not imply motion, as far as its absolute and intrinsic nature is concerned; […] time implies motion to be measurable; without motion we do not perceive the passage of Time” (Whitrow, Fraser & Soulsby 76). Barrow identifies Time with slow and steady motion, but he concludes that it is impossible to define Time without linking it to the steady and continuous motion of stars, the Moon, and the Sun (Whitrow, Fraser & Soulsby 76). As a result, the motion of celestial bodies can looks like the common thread between different definitions of time. Certainly, Barrow was not unique in his desire to link time to space shifts, but he was one of the first to recognize time as a mathematical concept. For Barrow as well as for his followers, Time was a linear mathematical function. It was associated with a circular line. Barrow viewed time as the concept independent of everything else, and as the concept that flew regardless of economic, social, and environmental changes. However, Barrow was not the only one trying to discuss time from scientific viewpoint.Numerous scientific theories have been developed to prove or deny the relevance of different time definitions. For example, Newton viewed time not as motion but as a universal instrument of measurement; according to his theory, time was not a relative but an absolute category (Brann 49). His ideas were later rejected by Leibniz, who was confident that Time was nothing else but a predetermined sequence of events; for Leibniz, events were the fundamental components of Time (Brann 56). In the variety of visions and ideas, none of them could become the basis for creating an objective theory of time. Time was always surrounded by a realm of myths and subjective opinions that lacked comprehensibility. It was not before Einstein that all previous assumptions have been reduced to nonsense, and it was not before Einstein that a completely new philosophy of Time has been developed. “It might appear possible to overcome all the difficulties attending the definition of ‘time’ by substituting the position of the small hand of my watch for ‘time’” (Brann 80; Seeman 104). Why watch? The truth is that it is virtually impossible to avoid subjectivity and relativity, when determining Time by watch. Also, it is impossible to guarantee synchronicity of all clocks and watches on the planet. The choice of the watch as the instrument of Time is not accidental, as far as it exemplifies the dramatic differences in perceptions, which individuals hold with regard to Time.Einstein’s beliefs about time are rooted in earlier theories, which linked time to the motion of bodies in space. Simultaneously, Einstein was the first to link Time to the speed of light and the notion of simultaneity. Where the movement of watch had to denote the process or the motion of space bodies, this very watch had to denote the simultaneity of things. In other words, through the prism of Time, each event had to be linked to each particular moment of Time, or to each particular position of the watch hands (Whitrow, Fraser & Soulsby 87). The use of the watch as the measure of time, however, was only possible for the events that took place in close proximity. Thus, linking the concept of time to the concept of watch was possible only for the events that took place at close proximity. In case of events that took place at different locations, the concept of the watch immediately lost its relevance.Does that mean that we cannot reconsider the concept of Time without tying it to the concept of the speed of light? Or does that mean that Einstein’s vision of Time is the most convenient and applicable of all Time theories? In reality, all time theories and assumptions are not without their fallacies. Time equally comprises rational and irrational features. From the rational perspective, time can be explained through the prism of space movements, or their sequence. Irrationally, time looks like a predetermined order of things, or their sequence that divides our lives into “before” and “after” and flows independently regardless of the major environmental or physical changes. In the light of numerous theories and assumptions with regard to time, it is impossible to limit the concept of time to rational or irrational considerations. Moreover, it is the balance of rational and irrational that may help create the single and the most relevant theory of time. Leibniz wrote that “Time is the order of existence of those things which are not simultaneous. Thus time is the universal order of changes when we do not take into consideration the particular kinds of change” (Seeman 77). Unfortunately, time is far from being universal but is still a measure of the order of changes, regardless of the nature of each particular change. From the differences and commonalities between philosophic and rational beliefs about Time, the latter comes out as the concept, which is closely tied to cosmology and the motion of celestial bodies around the earth, as well as the relative (and never absolute) measure of events and their sequences, with this relativity being integrally linked to the notion of light.ConclusionOver the course of the human history, dozens of philosophers and scientists sought to determine what Time is and what changes it produces on our vision of reality. Where philosophers held irrational beliefs about Time, scientists tried to link Time to mathematical concepts. Despite the differences, most of them viewed Time through the prism of cosmology and the motion of celestial bodies. Simultaneously, it was not before Einstein that Time ceased to be an absolute concept. As a result, through the major commonalities and differences in individual beliefs about Time, the latter stands out as a relative measure of events and their sequences, closely linked to the concept of cosmology and the motion of celestial bodies.