In addition to this (very good pill) I will add a distinction between types of "common law":
  1. common law : a law common to all, lex loci aka law of the place, oral tradition based on customs, morals & ethics
  2. Common Law : or British common law, not always friend of the people, plenty of atrocities committed under it, sometimes case law based on previous precedents
  3. The Common Law : a codified version of common law, often found in acts of parliament and constitutions, serving as alibi, give citizens subjects an impression of common law; sometimes criminal matters in civil law jurisdiction will be subject to The Common Law, due to lack of statutes and/or their regulations.
I know that many times we do not pay attention to how we write words, but in case you want to specify clearly which common law, is good to know these details.