I do not forget that nature works by laws; that the workings of nature are not accidental, but the result of certain causes which produce certain effects; so that the operations of nature produce an endless chain of cause and effect. Thus in the fall, because the sap flows downward in the tree, the fiber of the leaf’s stalk is gradually weakened, until the leaf by degrees loses its hold on the branch, and, because everything obeys the law of gravitation, falls to the ground. But where will it fall? That may depend upon the force and direction of the wind. It may happen that the wind is from the north or from the west; that its breath is soft, or that it blows a gale. I say it “may happen” so or so; for this is our habit of speech. When we don’t understand the cause from which an effect springs, we use the word “happen,” as if the affair were an accident or chance.