There are two basic kinds of law – statutory and common law.
Statutes are the laws passed by state and federal legislatures.
Federal law includes:
Rights guaranteed in the constitution. These are a “floor” but not a “ceiling.” In other words, states may pass laws that give their people more rights than are guaranteed in the constitution, but the states must provide their people at least these rights.
Example: The United States constitution has been interpreted to require that all indigent criminal defendants facing a possible sentence of 60 days or more have an appointed lawyer if they can’t afford them. The U.S. constitution does not require a free lawyer for appeals, but the states provide one anyway.
Federal laws also govern things considered too important to have variation among the states, or that concern the country as a whole. For example, it was long ago decided that it would be better to have one postal system, one armed forces system, and one type of money, rather than letting states create their own. Federal regulations also govern issues that are considered to affect everyone and that it’s important to have standardized, such as the testing of new drugs and regulation of air travel.
State laws include all the statutes that a state passes governing whatever they want to have rules about, as long as these statutes don’t violate the federal constitution or try to govern a subject that the feds already have a claim on. So, a state cannot have its own special laws on the cost of postage or the requirements to join the army.
The theory is that it’s better to allow the states to “experiment” with laws in various areas, and then maybe the more successful ideas might spread to other states. Areas of life governed by state law include:
Laws about schools and education.
Laws about marriage, divorce, and the rights of parents.
Criminal law – which behaviors are a crime, the punishments, the procedures.
Laws addressing state institutions, such as state parks, the state budget, the state police, and so on.
But, no matter how detailed these state and federal laws are, there are always new situations that aren’t covered by any law, or that require a court to interpret the laws on the books. Plus, people hate to lose, so they often appeal the result of a trial. The appellate courts then decide whether the trial judge made a mistake that requires reversing of changing the decision.
For example, under North Carolina law, once a court has decided who has custody of a child, the custody arrangement cannot be changed without a “substantial change in circumstances.” You can imagine how quarrelling ex-spouses fight over what is a substantial change of circumstances.
Let’s suppose that someone appeals a child custody determination and argues that since their ex-wife has joined the army, there is a substantial change of circumstances. What would you consider in deciding this? Whether she is stationed overseas or in the U.S.? Who else is in her household? Other factors?
Okay, so let’s suppose the appellate courts of the State of Confusion rule that when a parent enlists in the armed forces, this is automatically a change in circumstance that entitles the other parent to seek a change in custody.
That rule, whether it’s a good one or a stupid one, becomes the law in that state. Because this rule was announced by a court interpreting the statute, it’s called a “common law” rule. The “common law” is all the rules, holdings, and decisions of appellate courts. Statutes are laws passed by a congress, and the common law is found in decisions in appeals that interpret the statutes
So, if there is an outcry in the State of Confusion, maybe the state legislators in Confusion will pass a new law stating that “the trial court may not consider a parent’s service in the armed forces as a change of circumstances unless there is additional evidence showing that the parent’s service has caused a substantial change in the child’s daily life.” Then that statute trumps the common law.
But as soon as that law is passed, people will be back in court arguing over what is required to demonstrate that a parent’s enlistment has “caused a substantial change in the child’s daily life.” And round and round we go.