Augustine states that on earth, time is difficult to define. He writes that all creation seems to exist in time: the past, present, and future are the ways in which time is knowable to human beings. However, he argues that the past and the future, regardless of the presence of memory, do not exist: all we have is the present moment. He breaks that moment down into the smallest instance, and he cannot define what the present moment really means. This present moment cannot have space (for it is time), nor can it have duration, for once it has happened it is gone into the past. From this he posits that time doesn't truly exist, even though it seems to (because it can be discussed and measured). In this hopelessly negative argument, Augustine accepts that the notions of past, present, and future are useful for human beings.
The refutation of the existence of time is persuasive even today. The idea that God is the "beginning point" rather than the beginning in a temporal sense is particularly neat, though Augustine, as in so many things, owes a debt of gratitude to the Neoplatonists for this concept. Despite the muddled and convoluted form Augustine's arguments sometimes take, these arguments are useful not only to metaphysical philosophers, but to anyone who has ever pondered the first principles. Augustine is rigorous in that he takes nothing, not even the Bible, on pure faith. In true skeptical fashion, he is willing to question everything, and is determined to try to get to the base of any philosophical problem, no matter how remote or difficult.