English law is unique in that it is based on applying legal precedent to present and future decisions made by judges. A judge must follow past legal decisions made by higher courts but not necessarily those made by lower courts. English law is not based on a constitution and there is no codification of laws. However, there are unofficial publications that provide organized lists of current laws. Parliament has the power to create laws which are automatically considered valid and may not be reviewed by the courts. Only Parliament has the power to change a law.