Reasonable doubt is a legal concept used in criminal trials, where the prosecution must prove the accused is guilty beyond a reasonable doubt in order for a conviction to be made. This is the highest standard of proof in criminal law, and is based on a concept of moral certainty that the accused is guilty of a crime. There are two types of reasonable doubt: permissive, which means that the evidence is sufficient to support a reasonable doubt; and strict, which states that the evidence must be so strong that it is beyond reasonable doubt that the accused is guilty.