  Arguments from precedent are a prominent feature of legal reasoning. But what exactly is a ‘precedent’?  A precedent is the decision of a court (or other adjudicative body) that has a special legal significance. That significance lies in the court's decision being regarded as having practical, and not merely theoretical, authority over the content of the law. A decision has theoretical authority if the circumstances in which it was made (the identity of the decision-makers, those involved in arguing the case, the availability of evidence or time) provide good reasons for believing the decision to be correct in law. If there are good reasons to believe that an earlier case was correctly decided, and if the facts in a later case are the same as those in the earlier case, then there are good reasons for believing that the same decision would be correct in the later case. In some legal systems earlier decisions are, officially, treated in just this way: cases are cited to courts, but courts may only justify their decisions by reference to other legal materials such as legislation. As a consequence the decision in an earlier case is not in itself regarded as a justification for reaching a decision in a later  case.[1]