crim. law. The right to protect one’s person and property from injury. 2. It will be proper to consider, 1. The extent of the right of self-defence. 2. By whom it may be exercised. 3. Against whom. 4. For what causes. 3. 1. As to the extent of the right, it may be laid down, first, that when threatened violence exists, it is the duty of the person threatened to use all, prudent and precautionary measures to prevent the attack; for example, if by closing a door which was usually left open, one could prevent an attack, it would be prudent, and perhaps the law might require, that it should be closed, in order to preserve the peace, and the aggressor might in such case be held to bail for his good behaviour; secondly, if, after having taken such proper precautions, a party should be assailed, he may undoubtedly repel force by force, but in most instances cannot, under the pretext that he has been attacked, use force enough to kill the assailant or hurt him after he has secured himself from danger; as, if a person unarmed enters a house to commit a larceny, while there he does not threaten any one, nor does any act which manifests an intention to hurt any one, and there are a number of persons present, who may easily secure him, no one will be justifiable to do him any injury, much less to kill him; he ought to be secured and delivered to the public authorities. But when an attack is made by a thief under such circumstances, and it is impossible to ascertain to what extent he may push it, the law does not requite the party assailed to weigh with great nicety the probable extent of the attack, and he may use the most violent means against his assailant, even to the taking of his life. For homicide may be excused, se defendendo, where a man has no other probable means of preserving his life from one who attacks him, while in the commission of a felony, or even on a sudden quarrel, he beats him, so that he is reduced to this inevitable necessity. And the reason is that when so reduced, he cannot call to his aid the power of society or of the commonwealth, and, being unprotected by law, he reassumes his natural rights, which the law sanctions, of killing his adversary to protect himself. See also self-defense which is an alternate spelling.