So it seems certain that consciousness really does "butt in" on the chain of natural causation. And yet, just see in what position this leaves the scientist who is investigating life! Imagine if you can, the plight of a doctor who wanted to prescribe a diet for a sick person, if he knew that every piece of chicken and every piece of fish were free to decide of its own impulse whether or not it would be digested in the human stomach. But the plight of this doctor would be nothing to the plight of the chemist or the biologist or the engineer who was asked to do his thinking and his planning in a world containing a billion and a quarter human beings, each one a lawless agent, each one a source of new and unforeseeable energies, each one acting as a "first cause," and starting new chains of activity, tearing the universe to pieces according to his own whims. What kind of a universe would that be? It would simply be a chaos; there could be no thinking, there could be no life in it; there could be no two things the same in it, and no laws of any sort. So then we fall back into the hands of the "determinists," who assert one unbreakable chain of natural causation, and regard the human body as an automaton. We go back to the bio-chemist, who purposes some day to ascertain for us just exactly what molecules of matter in just what positions and combinations in the brain cells of William Shakespeare caused him to perpetrate a mixed metaphor. We go back to the belief that human beings act as they must act, because the clock of life, wound up and started, must move in such and such a fashion. But now, let us see what are the implications of that theory! Here am I writing a book, appealing to men to act in certain ways. Of course, I know that not all will follow my advice. Some will be foolish--or what seems to me foolish. Others will be weak, and will resolve to act in certain ways, and then go and act in other ways. But some will be just; some will be free; some will use their brains--because, you see, I am convinced that they _can_ use their brains! I am convinced that ideas will affect and stir them, in complete defiance of the bio-chemist, who tells me that they act that way because of certain chemicals in their brain cells, and that I write my book because of other chemicals, and that my idea that I am writing the book because I want to write it is a delusion, and that the whole thing is happening just so because the universe was wound up that way.