A more thorough explanation:

SI SIT INCOMPOS MENTIS, FATUUS, ET NATURALITER IDIOTA

SI SIT INCOMPOS MENTIS, FATUUS, ET NATURALITER IDIOTA is a Latin phrase used in Scots law. It refers to a situation where a person is of unsound mind, fatuous, and naturally an idiot. This phrase is used in an inquiry posed to a jury required to make an idiocy determination.

An example of the use of this phrase would be in a court case where a person is being evaluated for their mental capacity. If the person is found to be of unsound mind, fatuous, and naturally an idiot, they may be deemed incapable of making certain legal decisions or entering into certain contracts.

For instance, if a person with a severe intellectual disability is asked to sign a contract, they may not fully understand the terms of the agreement. In this case, the court may use the phrase SI SIT INCOMPOS MENTIS, FATUUS, ET NATURALITER IDIOTA to determine that the person is not capable of entering into a legally binding contract.

Another example could be in a criminal case where the defendant is being evaluated for their mental state at the time of the crime. If the defendant is found to be of unsound mind, fatuous, and naturally an idiot, they may not be held fully responsible for their actions.

Overall, this phrase is used to describe a person who is not capable of making certain legal decisions or being held fully responsible for their actions due to their mental state.