The harmonizing of legal administrative practice with the development of scientific concepts in the field of medicine is sometimes difficult. The law has to be understood by everybody, whereas scientific knowledge is too often considered the privilege of the educated few. Thus, the law must be simple and directly applicable, leaving for the expert, critical examination of causes and effects. When the definition of a situation depends upon physical findings, a decision can be made without very much difficulty as to how the law is to be interpreted; but in questions of behaviour interpretation of rules may be much more troublesome, and special care is required in drafting laws which define psychological concepts.