Which of the following is NOT a valid defense to a crime?

Ignorance of the law is typically not recognized as a valid defense to a crime. This principle is rooted in the legal maxim "Ignorance of the law is no excuse." Therefore, individuals are expected to be aware of the laws that govern their conduct, and claiming that one did not know an action was illegal generally does not absolve them of responsibility.

In contrast, self-defense is a valid defense that allows an individual to use reasonable force to protect themselves from imminent harm. Duress also serves as a valid defense, as it applies when an individual commits a crime because they were threatened with immediate harm unless they complied. Insanity can be a defense if it can be demonstrated that the individual was unable to understand the nature of their actions or did not know they were wrong due to a severe mental illness. These defenses recognize specific circumstances where a person's culpability may be reduced or negated, while ignorance of the law does not afford that same leeway.