Legal reasoning in the common law is based on rules adopted in binding legal precedents or authoritative although not binding rules. Some commentators claim that legal reasoning is analogy-based rather than rule-based, but a simple reading of common law cases makes it evident that common law courts seldom reason by analogy. Furthermore, in an experiment in which eighty-four common law cases were selected at random, only three reasoned by analogy. The answer as to why common law courts seldom reason by analogy is simple: a court would never reason by analogy if a case is governed by a rule, and the common law is thick with rules. Some other commentators claim that legal reasoning is based on a similarity. This claim is also incorrect, partly for the same reason and partly because if a prior case is identical to the case to be decided it will almost certainly have laid down a rule that governs that case, and if a prior case is only loosely similar to a case to be decided a court would normally adopt a new rule, because in that case it would need to make its reasoning clear.