In this remark St. Augustine in the 5th century AD drew attention to the fact that while time is the most familiar of concepts used in the organization of thought and action, it is also the most elusive. It cannot be given any simple, illuminating definition. According to those, such as Sir Isaac Newton, who adopt an absolutist theory of time, the answer to the former question is that time is like a container within which the universe exists and change takes place. Time's existence and properties are independent of the physical universe. Time would have existed even if the universe had not.
Time is held to be nonending, nonbeginning, linear, and continuous.
That time has these properties is established philosophically, without reference to scientific investigation. According to the rival relationist theory, time can be reduced to change. Also, investigating the properties of time is to be done scientifically. It has been realized in the 20th century that time cannot be treated in isolation from space. Consequently philosophers now tend to focus attention on space-time, conceived, after Einstein, as a continuum.