Properly devised and applied psychological tests may conceivably disclose the existence of mental powers and capacities unsuspected or neglected because overshadowed by strong inclinations in other directions; early knowledge of the possession of such capacities may easily direct their possessors into fields in which they can thrive and prosper and achieve far greater happiness and contentment than would ever be possible through a lifetime of striving to do that for which they are not fitted by inheritance. CHAPTER III WHAT THESE TESTS MEASURE The most natural question and one that is frequently asked is: “What, precisely, do psychological tests measure?” It is a question that is easier to ask than to answer. It is simple enough to say that mental tests are designed to measure the natural or inherent mental capacity of the individual, but in order to approach a clear understanding of just what this means we must first define what is meant by the term “mental capacity.” As a matter of scientific fact, the term “mental capacity” can hardly be regarded as accurate, although it is the best term we have to describe the qualities which determine the individual’s ability to perform acts requiring conscious thought. Psychological and biological science no longer regard the human mind as something different from or in any way apart from the human body. The idea that there is such an entity as a mind that operates even in the slightest degree without reference to and independent of the physical body must be dismissed, if we are to grasp clearly the principles and methods of mental tests. To the psychologist the mind is merely a specialized organ of the physical body. The intangible something, which is what is usually meant when persons speak of the human mind, is merely the sum of all the sensations, feelings, and judgments resulting from the delicate adjustment of an almost infinite number of nerve fibres which in themselves are a part of the physical body. One may have at birth a plentiful supply or a poor supply of potential nerve endings which are ready to be organized and coördinated by experience and training, but unless one has the opportunity to learn from study and experience, the desirable connections may never be developed.