The law of General Exceptions deal with specific circumstances which slightly favour the accused in a trial for an offence alleged to be done by him. Generally the prosecution has to prove the offence alleged against the accused. In the case of accused pleading general exceptions which exempt the accused from the larger punishment or absolve him of any punishment, the burden is upon him to prove the exceptional circumstances.
Necessity which is defined in Section 81 of the Indian Penal Code deals with an exception which excuses the offence. As per the section no act will be considered an offence even if it is done with the knowledge that harm will be caused, if the same act was done without any criminal intention. Such an act occurs when the person does the act to prevent any harm to person or property in good faith. The maxim 'necessitas vincit legem' which means 'necessity overcomes law' is the basis of this section.
The essentials in the above exception are as follows:
The act must have been done under good faith.
There must be knowledge of causing harm.
There must not be a criminal intention to cause harm.
The principle behind the section is that where a person meets with two illegal evil acts, one of which is indispensable, he may choose the lesser offence and not the greater. The law excuses such an action.
There is some similarity between the excuse of necessity and right of private defence as exception.
However as noted above, the burden is upon the accused to prove that the circumstance was so imminent that he has the excuse of doing the risk.