Ignorantia Juris Non Excusat
“Ignorantia juris non excusat” is based on the Latin Maxim “ignorantia legis neminem excusat” or “ignorantia juris, quod quisque, saire tenetur neminem excusat” which literally means “Ignorance of the law is not an excuse.”
The words mistake of law in the maxim can be interpreted in two ways. Primarily, it is that a person should know the existence of the law on a relevant subject and secondly, it also means what the contents of the law are. The maxim when elaborated states that ignorance of fact can be an excuse which might be entertained by the honourable judges as a defence however ignorance of a law is not acceptable as a defence for committing any wrong. For instance, if a legal heir is unaware of the fact that his ancestor is dead, this can be said to be ignorance of fact which might be excused, however, if a person murders someone and pleads not guilty by stating that he was oblivious of the law that killing someone is a crime, an offence under the Indian Penal Code, he will not be excused.
It is presumed by that maxim that every person of an age of discretion and of sound mind (Compos Mentis) is bound to know the law. Even though the legal maxim and its presumption sounds unfair, and absurd it still hold for two important reasons. Firstly, because if it is not as stringent as it sounds there is no limit to which this excuse may be used and lastly that it could be used in all cases.
In a case judged by Supreme Court it was concluded that since the honourable bench had also never heard of that law it was unlikely for the illiterate person living in a remote village to know it thereby instead of blindly applying the maxim they acquitted the person and did not impose penalty on him for violating the law.
Similarly, in the case of Commissioner of Income-tax v P.S.S. Investments P. Ltd  107 ITR 0001, the Hon’ble Supreme Court observed that “The intelligence of even those with legal background gets staggered in this continuous process of carving exceptions to exceptions. It seems more like a conundrum, baffling the mind and requiring special acumen to unravel its mystique. One can only wonder as to how the ordinary tax-payers, most of whom are laymen, can keep abreast of such laws. Yet the maxim presumes that everyone knows the law.”
To conclude, it can be said that mistake of law, if procedural may be considered by the honourable judges however if they are statutory it is difficult to be ignored unless the situations are peculiar as observed in the cases above.