Cannon Law vs Common Law

Sometimes layers trained in Common Law do not gasp the differences between Common Law and Cannon Law. The main difference between the two systems is well explained by Edward Peters in his essay "Least Amateurs Argue about Cannon Law: a reply to Patric Gordon brief agains Bp Thomas Daily"

I have encountered this attitude among common lawyers [ "cannon law is riddled with exceptions"] before but, being trained in the common law system myself, I think I understand what leads some of them so wrongly to his conclusion. Canonical legislation does not read like common law legislation for some very important reasons and common lawyers who would venture into canonical waters need to understand this before setting out. It is certainly not my intention to defend the felicity of every expression used in the Code of Canon Law but, if one aspect of the difference between canon law and common law needs {128} to be clearly understood, it is this: Common law is a system of judicial supremacy; canon law is a system of legislative supremacy.Grasp that, and one has the essence of the thing. [Emphasis in the original]

The key point is thus the following

Common law is a system of judicial supremacy; canon law is a system of legislative supremacy

This answers the following question: who has the authority to interpret what is the meaning of a given law? 

In the Common Law this power of interpreting the meaning of the written law resides in the courts. As a consequence a) the legislator, when writing the law, tries to put as much details as possible, to prevent and interpretation contrary to its goals; and b) the lawyers, when preparing for a case, would consult a vast literature of pervious court ruling in that matter. 

In the Cannon Law the power of interpreting the meaning of the written law resides with the legislative power. This is stated as follows in the 1983 CIC 16 § 1 “The legislator authentically interprets laws as does the one to whom the same legislator has entrusted the power of authentically interpreting.” And the proof that the courts have not the power to generically interpret the law is also states in the 1983 CIC 16 § 3 as follows: “An interpretation [of law] in the form of a judicial sentence or of an administrative act in a particular matter, however, does not have the force of law and only binds the persons whom and affects the matters for which it was given.” As a consequence of the supremacy of the legislator in interpreting matters of law, the cannon law articles tend to be shorter than the common law as they don't seek to deal extensively with all imaginable cases, and the few cases that may not be clear can be left to be decided by the ordinary Bishop or other authority. Another consequence of the supremacy of the legislative power is that cannon lawyers, when dealing with a disputable issue of which they want to assess the outcome,  they turn on to cannon law commentaries, and more recently also to the study of development of the cannons. For cannon lawyers therefore Cannon Law commentaries and the study of its development play a similar role than the books of court rulings plays for a common law lawyer. 

You can go to Peters' essay if you need more clarifications.