If we could list all the traits, each representing some one characteristic of human nature, and measure the amount of each of them possessed by a man, we could represent his nature--read his character--in a great equation. John Smith would equal so many units of this, plus so many units of that, and so on. Such a mental inventory would express his individuality conceivably in its entirety and with great exactitude. No such list has been made for any man, much less have the exact amounts of each trait possessed by him been measured. But in certain of the traits, many individuals have been measured; and certain individuals have been measured, each in a large number of traits. It is useless to recount the traits in which men have been found to differ. For there is no trait in which they do not differ. Of course, if the scale by which individuals are measured is very coarsely divided, their differences may be hidden. If, for example, ability to learn is measured on a scale with only two divisions, (1) "ability to learn less than the average kitten can" and (2) "ability to learn more than the average kitten can," all men may be put in class two, just as if their heights were measured on a scale of one yard, two yards, or three yards, nearly all men would alike be called two yards high. But whenever the scale of measurement is made fine enough, differences at once appear. Their existence is indubitable to any impartial observer. The early psychologists neglected or failed to see them precisely because the early psychology was partial. It believed in a typical or pattern mind, after the manner of which all minds were created, and from whom they differed only by rare accidents. It studied "the mind," and neglected individual minds. It studied "the will" of "man," neglecting the interests, impulses, and habits of actual men. The differences exist at birth and commonly increase with progress toward maturity. Individuality is already clearly manifest in children of school age. The same situation evokes widely differing responses; the same task is done at differing speeds and with different degrees of success; the same treatment produces differing results. There can be little doubt that of a thousand ten-year-olds taken at random, some will be four times as energetic, industrious, quick, courageous, or honest as others, or will possess four times as much refinement, knowledge of arithmetic, power of self-control, sympathy, or the like. It has been found that among children of the same age and, in essential respects, of the same home training and school advantages, some do in the same time six times as much, or do the same amount with only one-tenth as many errors. B. HUMAN NATURE AND SOCIAL LIFE 1. Human Nature and Its Remaking[65]