All human knowledge proceeds out of experience; we cannot know anything except by experience. All our reasoning is based upon generalised experience, all our knowledge is but harmonised experience. Looking around us, what do we find? A continuous change. The plant comes out of the seed, grows into the tree, completes the circle, and comes back to the seed. The animal comes, lives a certain time, dies, and completes the circle. So does man. The mountains slowly but surely crumble away, the rivers slowly but surely dry up, rains come out of the sea, and go back to the sea. Everywhere circles are being completed, birth, growth, development, and decay following each other with mathematical precision. This is our everyday experience. Inside of it all, behind all this vast mass of what we call life, of millions of forms and shapes, millions upon millions of varieties, beginning from the lowest atom to the highest spiritualised man, we find existing a certain unity. Every day we find that the wall that was thought to be dividing one thing and another is being broken down, and all matter is coming to be recognised by modern science as one substance, manifesting in different ways and in various forms; the one life that runs through all like a continuous chain, of which all these various forms represent the links, link after link, extending almost infinitely, but of the same one chain.