A legal duty is an obligation imposed by the law. Failure to fulfill such a duty can result in criminal or civil sanctions. Legal duties are distinct from moral or ethical duties; while a duty may be both legal and ethical, only legal duties are enforced by the justice system.
Legal duties can be created in several ways and by several different types of law. Within countries called common law countries — such as the United Kingdom and the United States — previous cases brought before a judge can create a legal duty. Legislation written by the state, local or county government can also impose a legal duty on individuals within the borders that the law applies to.
There are also two general classifications of legal duties: those duties where a breach is criminal and subject to criminal sanctions and those duties where the breach is punishable under civil law. There may be some overlap and certain behaviors may be governed both by criminal and civil law. This means that certain actions may be subject to both civil and criminal penalties.
One legal duty, for example, may be the duty not to kill someone by recklessly driving a vehicle. The law can impose criminal sanctions for violating that duty — the bad driver who causes the death may be arrested and tried for vehicular manslaughter and sent to jail. The law can also impose civil sanctions — the estate of the driver can sue for wrongful death in civil court and recover monetary penalties.
In most cases, the duties imposed under the law are duties to refrain from doing certain behaviors. The law, for example, imposes a duty not to steal, not to commit fraud, not to cheat on taxes, not to kill, and not to do many other socially unacceptable behaviors. In addition, though, the law may also impose duties to do certain things. Civil law, for example, imposes a duty that everyone act with reasonable care to refrain from harming others; failure to act with reasonable care leads to tort lawsuits.
When a person violates a legal duty, punishment occurs according to the type of violation. This is the key difference between legal duties and other types of duties, such as moral or ethical duties. While it may be immoral to lie to a parent about coming home after curfew, it is not illegal; however, it is both immoral and illegal to lie to the tax collector about the amount of income earned in a year.