The development of law is divided into three eras. In the pre-historical era, societies were based upon clans, tribes, or kinship, and law was derived from social norms and values. The enforcement of these customary laws was informal but effective. Judges were tribal chiefs or elders. This is a form of Khadi justice, in which there is significant reliance on religious and supernatural beliefs. Khadi justice is very effective in homogenous societies. The early historical era included the development of several written legal codes, which had a profound influence upon the U.S. legal system. There was an emergence of different roles within the legal system, including groups to enact, enforce, and judge laws. The modern era included the Renaissance and Age of Enlightenment, as well as a reemergence of natural law.
Penal law defines the activity that a society prohibits through criminal laws. Compensatory law consists of civil law disputes. Therapeutic law provides help for an offender's behavior. Conciliatory law attempts to provide a win-win outcome through conflict resolution.
Civil law legal systems are modeled after Roman and Napoleonic codes. Civil law systems include a lack of judge-made law; rights of the community; a complete written code; an inquisitorial legal system; and decisions by judicial panels. Common law legal systems include framework documents interpreted by judicial rulings; rights of the accused; customary law and case precedent; an adversarial legal system; and decisions by juries.
Civil law deals with disputes between private parties. The parties are the plaintiff, who initiates the suit, and the defendant, against whom the suit is brought. Criminal law deals with offenses against society. The parties are the prosecutor, who brings the case, and the defendant, against whom the case is brought. Civil and criminal procedures govern the dispute resolution process.
Substantive law defines crimes, and procedural law tells how a case must be processed. Sources of law include the common law, constitutional law, statutory law, case law, and administrative law.
Crimes are classified by their evilness into mala in se crimes, which are evil in themselves, and mala prohibita crimes, which are wrong because there is a law prohibiting them. Crimes are classified by their seriousness into felonies, which are serious crimes that may be punished by at least one year in prison, and misdemeanors, which are less serious crimes that may be punished by jail time of up to one year. The state is responsible for proving all elements of a crime, which include the mens rea, actus reus, and concurrence.
Inchoate offenses are crimes in which the offense is not completed. This includes conspiracies, solicitations, and attempts. The two types of defenses are justifications, in which the defendant's actions were not legally wrong, and excuses, in which there was an extenuating circumstance that excuses the behavior. Justification defenses include self-defense and necessity. Excuse defenses include duress, entrapment, infancy, insanity, and intoxication. The primary types of crime are crimes against persons, crimes against property, crimes against public order, and other offenses.