A stone falls and we ask, why? This question is possible only on the supposition that nothing happens without a cause. I request you to make this very clear in your minds, for whenever we ask why anything happens, we are taking for granted that everything that happens must have a why, that is to say, it must have been preceded by something else which acted as the cause. This precedence and succession are what we call the law of causation. It means that everything in the universe is by turn a cause and an effect. It is the cause of certain things which come after it, and is itself the effect of something else which has preceded it. This is called the law of causation and is a necessary condition of all our thinking. We believe that every particle in the universe, whatever it be, is in relation to every other particle. There has been much discussion as to how this idea arose. In Europe, there have been intuitive philosophers who believed that it was constitutional in humanity, others have believed it came from experience, but the question has never been settled. We shall see later on what the Vedanta has to say about it. But first we have to understand this that the very asking of the question "why" presupposes that everything round us has been preceded by certain things and will be succeeded by certain other things.