There is a power to words associated with the present. The power of 'focusing on today', 'doing it today', 'only today', and all such phrases meant to increase our productivity or mindfulness. The past and future are illusions, these philosophies tell us. The only reality is the present and inside the present is where our minds should live and so we must live for today.
But, of course, today is not the present. Some portion of it remains in the future and nearly all the rest is in the past. Whatever is left is the present, but what is that? The present is a dividing line and that line can be narrowed infinitely, from today to this minute to this attosecond, and as the line vanishes into nonexistence what are we left with? The past and the future, two non-overlapping, bounded but infinite sets. No point in time can be given that is in both sets, but is it possible to give a point that is not in one of them? Answer with 'now' and by the time you have finished the word it your speaking it is now the past. Is there no point to be found outside these sets? Then the present is the illusion and reality is the past and future. But the present cannot be an illusion, comes the objection, after all that is where we live. That is where the 'I', the one that is even now typing these words, exists. It lives there, in that vanishing line that is the present. If that is an illusion then what is the 'I' that is typing? It must be an illusion as well. I feel that I have thoughts in the present but if there is no present then there are no thoughts and what proof can I give to refute this? That I am thinking now? The riddle is not solved by thinking the word anymore than saying it. I can offer only my memories of thinking. Only with the past can we prove the present, and how can one prove the past?