The theory of common law is that there are principles of justice that arise naturally from the biological and social nature of humanity. I have sometimes discussed that in terms of there being an (unwritten) constitution of nature, and a subordinate (unwritten) constitution of society, to which there is a subordinate constitution of the state (society in exclusive control of a territory), and a further subordinate (probably written) constitution of government (the document adopted in 1789 for the U.S.). See Social Contract and Constitutional Republics.
In this concept what a court does when it has to decide without a legislative enactment (written constitution, statute, etc.) is to discover those natural principles applicable to the case and its issues. Court precedents are therefore a history of such discoveries (called “findings”) in similar cases that are respected on the assumption that the previous courts did a good job of discerning the principles. In this sense, common law courts are something like a peer-review process in scientific fields , in which claims of discoveries by scientists are subjected to examination to determine whether they stand up to challenge, and past scientific discoveries are accepted until refuted by a later discovery.
So while the term “common law” goes back to the 11th century in England, the concept is much older, and was discussed in ancient Hebrew, Greek, and Roman law, as well as the legal traditions of other lands and peoples.
The distinction is important. In theory, the judge and jury are not “making” law. That would be legislation, and that is not within their jurisdiction. It is “finding” the underlying principles of justice that presumably govern all human societies, whether some of them know it or not.
By the 17th century, the system of common law in England was becoming problematic. There were just too many precedents, and it was usually possible to find a supporting precedent to support any position litigants might take. Lawyers could spend a lifetime reading the record of old cases and never cover them all. Attempts were made to codify common law in legal treatises, such as those of Bracton, Britton, Hugo Grotius, Francis Bacon, Edward Coke (pronounced “cook”), Thomas Hobbes, Samuel Rutherford, Samuel Pufendorf, John Locke, Algernon Sidney, Bynkershoek, Burlamaqui, Thomas Rutherforth (online edition in progress), Vattel, and Blackstone. However, this only led to conflicting schools of thought on the subject.
The demand for codification and simplification was one of the factors driving the emergence of the English House of Commons as that country’s supreme lawmaking body. However, without a single, coherent written constitution of government, other than a collection of enactments that had special weight by tradition, Commons functioned as a kind of ongoing constitutional convention, concerning which it came to be said, “No man’s life, liberty, or property are safe while [Commons] is in session.”
This problem is precisely what caused tension with the British North American colonies, and ultimately to the break and the independence of the United States. Coming out of that experience without a written constitution of government, and comprehensive statutes, the new country chose to abandon so much reliance on tradition and the common law, and adopted written constitutions for each state and then for the Union. They did not, however, discard it altogether. The written constitutions incorporated the nonconflicting parts of what had then become the American branch of common law (Camdenian rather than Mansfieldian), including almost all the definitions of legal terms.
So the U.S. Constitution is written in the language of the American common law, and I strongly advise modern students to approach the Constitution as though they were learning a foreign language. Contrary to what many think, much of the Constitution is not really written to be understood by ordinary, non-legal-educated people. Terms like “due process” and “jury” were terms of legal art with a vast body of cases and treatises behind them. Americans in the Founding Era were much more law-literate than are people today, but even the Founders had to hit the books mentioned above to find out what they were saying when they drafted the Constitution. So must we to understand what they wrote. There are no shortcuts.
Jury “nullification” did not really come into being with the 1670 Trial of Penn and Mead and Bushell’s Case. Those cases only solidified what had already become established as a foundation principle of common law, although until them there was much judicial practice in conflict with the principle. It is to noted that it was also already established that arguments on issues of law were to be made in the presence of the jury, and not just in the privacy of the judge’s chambers, a principle confirmed as late as Stettinius v. United States, 22 F. Cas. 1322 (1839); 5 Cranch C.C. 573, which has never been overturned (although it is now uniformly ignored).