Skepticism and Time
We can’t be certain the ordinary world of material objects exists: we might be brains in a vat or perpetually dreaming. We can’t be certain that space exists, at least in the form we think of it, for the same reasons. But what about time? We are familiar with skepticism with respect to the contents of time: the world might have been created ten minutes ago and have a very different history from the one we suppose. But might the past not exist at all? Might the future be a figment? What about the present—does it too fall to the skeptic? In the case of the present things look more hopeful: we can know for certain that it exists. How? By a version of the Cogito: if I am thinking now, then there must be a now for me to think in. Every occurrence needs a time in which to exist. Nothing happens without a time in which it happens. Even if I am only dreaming, my dream needs a time to occur in. Thus, we can confidently assert: “I think, therefore the present time exists”. There is no epistemically possible world in which I am thinking but there is no time. What the nature of this time is we may not know, but we know at least that the present moment is real: an existent thing falls under the concept the present, viz. a certain temporal moment. But the Cogito by itself doesn’t take us any further into time: maybe the present time exists but not past or future times. These are distinct existences, after all.
However, on reflection we can deduce the past and the future from the present: for what is present will soon be past and was once future. There can be no present without a past and future. It is a necessary a priori truth that a present moment exists within a series of moments some of which are in the past and some in the future. This follows from the fact that time flows, i.e., moments pass from future to present to past. No moment can be stuck in the present, incapable of becoming past and never having existed in the future. Every moment of your life was once a future moment and will become a past moment—as sure as eggs are eggs (a plain tautology). So, the present contains the seeds of the past and the future: at the moment you think “I think” that moment quickly moves into the past and was once a future moment. Thus, if we combine the temporal Cogito with this logico-metaphysical fact about time, we can deduce the result that past times and future times indubitably exist. What happens in or at these times is not certain, but that they exist (those times) is certain. Time might itself be relative or absolute, a matter of mechanical clocks or of God’s eternal mind, discrete or continuous, infinite or finite—but at least we know that it exists. Time logically follows from consciousness: the one kind of existence leads inexorably to the other. This is something. Matter doesn’t follow, space doesn’t follow, numbers don’t follow: but time does. Time is one of life’s great certainties. Odd that Descartes didn’t make more use of this truth. We don’t need God’s assistance to know that time exists; it is built into the very nature of experience. I can never say, “For all I know, time doesn’t exist”.
 We might be able to get from consciousness to matter, space, and even numbers by constructing clever philosophical arguments, but in the case of time we don’t need such ingenuity—time is written right into consciousness as a surface feature. Not the impression of time, mark, but time itself.