Sources of the Law

Fundamental Cases on the Fourth Amendment

Adam J. McKee


The United States is a common law country.  This means (among other things) that the laws of the United States are not presented in the form of static legal codes.  Rather, they are an evolving body of law based in large part on the doctrines set forth by judges.  This judge made law is presented in the cases that these judges decide.  A salient feature of this system is that the law can change and adapt as old doctrines are applied to new factual situations as society changes over time.

Another salient feature of American law is the governmental system of dual federalism.  Dual federalism refers to the fact that there are two levels of government: There is one complete system of government at the Federal level, and another complete system of government at the state level.  This means that both levels of government have separate and distinct legal systems.  There are some points where federal authorities have oversight in state law and legal practice, which can complicate the task of conducting legal research.

The dual court system in the United States is not equal in authority or workload.  The vast majority of criminal cases (around 95% of them) are prosecuted in state courts.  Some counties in the United States prosecute more cases in any given year than the entire federal court system.

Success in a procedural law course requires that you know the major sources of law (both primary and secondary), and how to find those sources.

Throughout the process of learning the law, you must also develop a competent legal vocabulary.  As with any profession, law has its own jargon and terms of art.  To understand the law once you find it, you need to be able to read and comprehend it.  This requires a commitment to not only learn the process of legal research, but the special language that goes along with it.  If you neglect these critical tasks, you will not perform well.  Because of our common law tradition, many legal phrases are of Latin origin.  This means that they will not be familiar terms; you must make the extra effort to commit these to memory.  Perhaps more problematic for some students is the fact that legal documents tend to use everyday words in very special ways.  Take care to note these special meanings that words take on in the legal context.  One of the first legal research tools that you should master is the legal dictionary.  There are many different versions of these, and several good ones are available online free.

It is important to realize that no single person knows the law.  Police officers, paralegals, lawyers, and judges must know basic legal principles to do their jobs, but the law is far too dynamic and expansive to ever really know.  What these professionals have in common is an ability to find the law that they need, to analyze it, and to apply it to factual situations.

As previously discussed, dual federalism means that there are two distinct legal systems in the United States.  There is a federal system complete with an executive branch that enforces the federal laws, a judicial branch that interprets the federal laws, and a legislative branch that makes the federal laws.  Of course, in any common law jurisdiction, appellate judges play a large role in making laws as well.  The government of every state mirrors these roles and processes.  This means that to be a competent legal researcher, you must be able to navigate the myriad legal documents that both of these levels of government entities produce.  In other words, you must learn to research the laws of the United States, as well as those of your individual state.  There are no legal resources that cover all laws.  You will need to master a separate set of resources to conduct legal research at each level of government.

No matter whether you are researching federal law or state law, you will note some important similarities that are common to the federal legal system and that of every state.  These distinct legal systems are often referred to a parallel because they operate distinctly, but in very similar (sometimes overlapping) ways.  Each of these systems derives its law from four basic sources: Constitutions provide the supreme law of the land.  In addition, there are legislative enactments (statutes), administrative rules and regulations, and judicial decisions (case law).

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Last Modified: 07/30/2018


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