Distinguish between the following: Mistake of Fact and Mistake of Law

Mistakes are of two kinds: (i) mistake of law, and (ii) mistake of fact. If there is a mistake of law of the land, the contract is binding because everyone is deemed to have knowledge of law of the land and ignorance of law is no excuse ( ignorantia juris non-excusat ). But mistake of foreign law and mistake of private rights are treated as mistakes of fact and are excusable. The law of a foreign country is to be proved in Indian Courts as ordinary facts. So, mistake of foreign law makes the contract void. Similarly, if a contract is made in ignorance of private right of a party, it would be void, e.g., where A buys property which already belongs to him.