There is, besides, a second obstacle. However difficult it may be to investigate the nature and causal connections of mental phenomena, everybody has a superficial knowledge of their external manifestations. Long before these phenomena were considered scientifically, it was necessary for practical human intercourse and for the understanding of human character, that language should give names to the most important mental complexes occurring in the various situations of daily life, such as judgment, attention, imagination, passion, conscience, and so forth; and we are constantly using these names as if everybody understood them perfectly. What is customary and commonplace comes to be self-evident to us and is quietly accepted; it arouses no wonder at its strangeness, no curiosity which might lead us to examine it more closely. Popular psychology remains unconscious of the fact that there are mysteries and problems in these complexes. It loses sight of the complications because of the simplicity of the names. When it has arranged the mental phenomena in any particular case under the familiar designations, and has perhaps said that some one has “paid attention,” or has “given free rein to his imagination,” it considers the whole matter explained and the subject closed. Still a third condition has retarded the advance of psychology, and will probably long continue to do so. Toward some of its weightiest problems it is almost impossible for us to be open-minded; we take too much practical interest in arriving at one answer rather than the other. King Frederick William I was not the only person who could be persuaded of the danger of the doctrine that every mental condition is governed by fixed law, and that in consequence all of our actions are fully determined--a doctrine fundamental to serious psychological research. He believed that such a teaching undermined the foundations of order in state and army, and that according to it he would no longer be justified in punishing deserters from his tall grenadiers. There are even to-day numerous thinkers who brand such a doctrine dangerous. They believe that it destroys all possibility of punishment and reward, makes all education, admonition, and advice meaningless, paralyzes our action, and must because of all these consequences be rejected.