Common laws are mainly describe as laws designed by the judges and not by the parliament. Just as the judges do consider that both criminal as well as civil matters, they do make decisions, deliver rulings and do develop precedents. Considering it altogether, I would say that these are the things which contribute together to design a common law. On the other hand, a good deal of civil law like for example, the torts and the negligence primarily initiated as common law rules and later it was differentiated.