Under what condition is the defense of "mistake of fact" applicable?

The defense of "mistake of fact" is applicable when the mistake negates the defendant's intention or mental state necessary for a crime to have been committed. In criminal law, many offenses require a specific intent or knowledge regarding the act being committed. If a defendant mistakenly believes a certain fact to be true—such as thinking an object they took was theirs—the misunderstanding can demonstrate that there was no intended wrongdoing. The effectiveness of this defense relies on the idea that the defendant acted without the required intent due to their mistaken belief about the circumstances surrounding their actions.

This principle is built around the foundational notion of mens rea, or "guilty mind," which is essential to establishing criminal liability. By showing that their belief was genuine and reasonable, the defendant can argue that they should not be held criminally liable for the act in question. Thus, a mistake of fact can serve as a valid defense if it can be shown that it negated the required intent for a conviction.