Criminal is a term defining a suspected or known breach of a society's laws, as determined by that society's legislative and judicial structure. The legislative branch of government is responsible for enacting laws defining what is to be considered criminal, and the judicial branch is responsible for interpreting those laws. Technically the term 'criminal' has no meaning except as it relates to enacted laws under a criminal code, as opposed to a civil code of law. However, it is also popular usage to brand as criminal any person or action which breaks the unwritten rules of a society.
A person is defined as a criminal once a court of law finds him guilty of having broken a criminal code law. (Those who break civil and contract law are not strictly considered to be criminals.) Ideally, the court of law tries to determine the truth of the matter. However, whether the person has actually broken the law is immaterial. What matters is the verdict of 'guilty.'
An action may be considered criminal before it is known whether the person who committed the action is a criminal. For example, causing someone to come to harm is a criminal action, but if a court of law finds that the person who caused this could not have been reasonably aware that his action would cause harm, he is not a criminal. In the same way, ignorance of the law does not excuse a person from being a criminal, but inability to comprehend the law might. Intent does not change the criminal label, only the specific law which has been broken.
In the strict legal sense, a person who is found incapable of discriminating between right and wrong cannot be convicted of a criminal act. This usually applies to young children, to the mentally handicapped, and to people found criminally insane.
In fact, now that insanity is no longer a medical term, the only valid meaning of insanity is the legal distinction of whether a defendant had the ability to distinguish right from wrong at the time of committing the criminal act. Some jurisdictions additionally require that the defendant was not in control of his actions at the time of the crime. It is possible to find a person criminally insane at the time of the crime without judging on current sanity, such as a person who suffered a serious psychotic episode at the time the crime was committed. In all cases where mental handicap or criminal insanity is suspected, the defendant is examined by psychiatrists for fitness to stand trial, for assessment of any underlying cognitive condition, and (if found not guilty due to insanity) for ongoing psychiatric treatment until the defendant is determined to no longer be a threat to society or himself.
Some victim families believe that all criminal acts are caused by a person who is criminally responsible. To these families, there is no excuse for one's actions due to criminal insanity, mental handicap, or youth. If a criminal act has been committed, a criminal must be punished for it.
One situation where judicial findings are changing in this direction is that of acts committed while drunk. The reasoning is that although the person may not be in control of their actions at the time of being drunk, he would reasonably have been able to foresee that getting drunk would reduce inhibitions, potentially leading to criminal acts such as drinking and driving, and make prior arrangements accordingly.
What is considered criminal changes based on local perspective. This is most apparent when traveling to another country. For example, in Saudi Arabia, possession of alcoholic beverages is a criminal act, something which continually trips up tourists and foreign workers. Criminal legislation and enforcement can very even from state to state, either because of different priorities or because of hidden corruption.
What is considered criminal can also change locally, even over short periods of time. Abortion and euthanasia are two areas where societal mores are divided, but so closely balanced in numbers that whichever side currently has the legislative or judicial edge, and therefore the power to enact or interpret law, keeps changing. Consequently the law reflects the societal mores of whoever has the power at the time, usually with a 10-20 year lag. This lag represents the time required to identify the problem, draw up the new law, and pass it through all the levels of government. This lag has proved a great difficulty in dealing with designer street drugs, which are developed faster than the law can criminalize them.
Slightly less controversially, there is an ongoing debate on whether possession of marijuana should be considered a criminal action, whether it should be decriminalized, or even whether it should be made legal. To decriminalize marijuana would not make it legal. It would only remove possession of marijuana from the criminal code of law.