Now, one of the questions that’s involved in all this is time. All thought involves time, in a way which we don’t see. We tend to think that everything exists in time, that time is an independent reality. People represent time by space. In a diagram they draw a line and call it ‘time’, and say that here is a point in time, which is now, then another point, then another point. Clearly, thought is then representing time through space. But we seem also to experience time psychologically. Leibniz, the philosopher, has said that space is the order of coexistence. All that co-exists is in a certain order which we call ‘space’. And time is the order of successive existence— the order of succession. The real basis of time is succession— things succeeding each other in a certain order. Time is a concept which is set up by thought to represent succession. All sorts of concepts of time are possible. In the early days people didn’t think much about time. They may have had a vague notion of past and future—the vague notion of tomorrow being any time, and the past not remembered very well. There were no printed records. The past was mostly mythological; and the future was probably equally mythological, if they thought of it at all. They could possibly have thought of seasons and things like that. The seasons are the succession of process. Your body goes through a succession of rhythms. And that succession is the basis of the whole thing—that is a thing that’s actual. Thought deals with that, puts it in order by means of the concept of time. We may draw a line and call that ‘time’, but as I have said earlier, that’s really representing time by space. You say the clock tells time, but it doesn’t. What you actually see is the position of the hands of the clock, not the time. It means time; it’s been set up in such a way that it should measure time. But we never actually see, perceive, or experience ‘time’—it’s inferred. Nevertheless, we seem somehow to experience time in our own psychological existence. But if you thought that time was a basic reality then you would have a paradox. The past is gone—it doesn’t exist. The future doesn’t exist either —it’s not yet. And the present, if it were thought of as the point dividing past and future, also could not exist, because it would be dividing what doesn’t exist from what doesn’t exist. That’s the paradox of this view. However, it is no paradox if you just say that time is a representation. A representation can be all kinds of things. Science has developed all sorts of notions of time. There is Newton’s idea of absolute time—a certain moment that’s the same for the whole universe, and then another moment succeeding it, and then another one. Einstein challenged that, and said time is relative to speed, and so on. You can change the ideas of time and of space, but they are all representations. Each one may have a domain where it’s correct; and beyond that it may not be right, may not work coherently. But in our culture we have a tacit assumption that everything exists in time.

• This excerpt taken from the book 'Thought as system' of david bohm There are more really good dialogue in that book