In California, an individual may use a knife in self-defense if they reasonably believe that they or someone else is in imminent danger of being killed or suffering great bodily harm. However, the use of a knife in self-defense must be proportionate to the threat faced, meaning that deadly force can only be used in response to an imminent threat of deadly force. Additionally, the individual using the knife must not be the initial aggressor and must have exhausted all other reasonable means of self-defense before resorting to the use of deadly force.

It is important to note that the use of a knife in self-defense is a complex legal issue and each case is unique. If you are faced with a self-defense situation, it is recommended that you consult with an experienced criminal defense attorney who can help you navigate the legal system and ensure that your rights are protected.