So William James took up the burden of proof some thirty years ago, and assured a doubting world of men and women that there were laws in the realm of mind as certain and dependable as those applying to the world of matter--men and women who were not at all sure they had any right to get near enough the center of things to see the wheels go round. But today thousands of people are trying to find out something of the way the mind is conceived, and to understand its workings. And many of us have in our impatient, hasty investigation, self-analytically taken our mental machines all to pieces and are trying effortfully to put them together again. Some of us have made a pretty bad mess of it, for we tore out the screws and pulled apart the adjustments so hastily and carelessly that we cannot now find how they fit. And millions of other machines are working wrong because the engineers do not know how to keep them in order, put them in repair, or even what levers operate them. So books must be written--books of directions. If you can glibly recite the definition above, know and explain the meaning of "mental life," describe "its phenomena and their conditions," illustrating from real life; if you can do this, and prove that psychology is a science, _i. e._, an organized system of knowledge on the workings of the mind--not mere speculation or plausible theory--then you are a psychologist, and can make your own definitions. Indeed, the test of the value of a course such as this should be your ability, at its end, to tell clearly, in a few words of your own, what psychology is. The word _science_ comes from a Latin root, _scir_, the infinitive form, _scire_, meaning to know. So a science is simply the accumulated, tested knowledge, the proved group of facts about a subject, all that is known of that subject to date. Hence, if psychology is a _science_, it is no longer a thing of guesses or theories, but is a grouping of confirmed facts about the mind, facts proved in the psychology laboratory even as chemical facts are demonstrated in the chemical laboratory. Wherein psychology departs from facts which can be proved by actual experience or by accurate tests, it becomes metaphysics, and is beyond the realm of science; for metaphysics deals with the realities of the supermind, or the soul, and its relations to life, and death, and God. Physics, chemistry, biology have all in their day been merely speculative. They were bodies of theory which might prove true or might not. When they _worked_, by actually being tried out, they became bodies of accepted facts, and are today called sciences. In the same way the laws of the working of the mind have been tested, and a body of assured facts about it has taken its place with other sciences.