What are the main differences between the civil and the common law systems ?

The majority of legal authors divide the legal systems in the world into two mains groups : the common law on the one hand and the civil law on the other hand . The most interesting is that when you try to find definitions for those words, you often find the basic definition and then as a conclusion you are told to distinguish the two systems. For instance, we can look at the definitions given by Britannica Encyclopedia for those two notions. civil law is defined as « a body of law developed from Roman law and used in continental Europe and most former colonies of European nations, including the province of Quebec and the U.S. state of Louisiana... The basis of law in civil-law jurisdictions is statute, not custom; civil law is thus to be distinguished from common law » . Then, common law is defined as « a body of law based on custom and general principles and that, embodied in case law, serves as precedent or is applied to situations not covered by statute. common law has been administered in the courts of England since the Middle Ages; it is also found in the U.S. and in most of the British Commonwealth. It is distinguished from civil law » .
Since those two systems are both used in the European Union, it might be interesting to look at their differences concretely. So, here we will focus on the main differences between civil and common law as define above. We will concentrate our discussion on the civil and common law as used on the European continent. Rather than focusing on each differences which will lead us to a descriptive listing, we will adopt an evolutive approach. Thus, we will look at the historical background of each systems and how it has influence their actuals characteristics (I). Then, we will focus on the main difference between civil and common law, that is to say the legal thinking, notwithstanding the fact that they always have the same purpose : regulate and harmonize the human activity . (II)