The doctrine assumes that the law in question has been properly published and distributed, for example, by being printed in a government gazette, made available over the internet, or printed in volumes available for sale to the public at affordable prices.
In the Criminal Law, although ignorance may not clear a defendant of guilt, it can be a consideration in sentence, particularly where the law is unclear or the defendant sought advice from law enforcement or regulatory officials. For example, in one Canadian case, a person was charged with being in possession of gambling devices after they had been advised by customs officials that it was legal to import such devices into Canada. Although the defendant was convicted, the sentence was an absolute discharge.
In addition, there were, particularly in the days before satellite communication and cellular phones, persons who could genuinely be ignorant of the law due to distance or isolation. For example, in a case in British Columbia, a pair of hunters were acquitted of game offenses where the law was changed during the period of time they were in the wilderness hunting. In reaching this decision, the court refused to follow an early English law case in which a seaman on a clipper before the invention of radio was convicted even though the law had been changed while he was at sea (Bailey (1800) Russ & Ry 1).
The essential public character of a law requires that the law must apply to anyone in the jurisdiction where the law applies. Thus, no one can justify his conduct on the grounds that he was not aware of the law.
Generally, a convention exists (by some called "the essential preliminary rule") by which the laws are issued and rendered accessibile by methods, authors and means that are simple and well known: the law is readable in certain places (some systems prescribe that a collection of the laws is copied in every local city council), is made by certain authorities (usually sovereign, government, parliament, and derivative bodies), and enters into effect in certain ways (many systems for instance prescribe a certain number of days - often 15 - after issue). This is commonly intended as a constitutional regulation, and in fact many constitutions or statutes exactly describe the correct procedures.
However, some recent interpretations weaken this concept. Particularly in civil law, regard can be had to the difficulty of being informed of the existence of a law considering the lifestyle of the average citizen. On the penal side, the quality of the knowledge of the law can affect the evaluation of the animus nocendi or the mens rea, in that certain subjective conditions can weaken personal responsibility.
The theme was widely discussed, also for political reasons, at the time of the Enlightenment and in the 18th century, given the heavy proportion of illiterate citizens in European countries (who would have some difficulties being aware of all the laws in a country). It was then argued that both the presumed knowledge and the heavily increasing corpus of national legislation were working in favour of lawyers rather than citizens. (The equivalent modern day claim being that the law is a trade secret and the public process a business owned and operated by the legal profession.)
In recent times, some authors have considered this concept as an extension of (or at least as analogous to) the other ancient concept (typical of criminal law) that no one can be punished under a law that was issued after the action was committed (non-retroactivity of the law. See ex post facto). This interpretation is however disputed, given that the matter would hierarchically more properly refer to a constitutional doctrine rather than to a civil or penal one.
Some modern criminal statutes contain language such as stipulating that the act must be done "knowingly and wittingly" or "with unlawful intent," or some similar language.