"In its present state of development psychology must be thought of as a young science. There is only one field in which it is relatively well established and in which it has advanced steadily: this is the psychology of sensation and perception. The scientific character of this field is fully recognized. Its findings are based almost entirely on experimental evidence, and even when its theories are in conflict one feels that as far as method is concerned it stands on relatively firm ground. The situation is different with the psychology of will, of needs, and of personality despite the fact that these fields have always attracted popular interest. As recently as fifteen years ago it was assumed that they, by their very nature, were not amenable to scientific methods. The little experimental work that had been done seemed too artificial and abstract to give an insight into the real processes. It was generally accepted that experimental investigations of these elusive and highly complicated processes were intrinsically impossible, at least in so far as human beings are concerned. Thus in Europe these problems were treated in a half-literary, half-philosophical way, and in America the tendency was to study individual differences by means of tests."