Force majeure
It would not be a valid contract. A contract to break the law is illegal.
No, a contract cannot supersede the law. The law always takes precedence over any agreements made in a contract.
Private laws are those that do not apply to everyone. An example of private law is a contract. As long as it is not illegal, you can contract for many things or you contract away your rights.
Contract law is just a body of law regarding... well... contracts.
Generally, the action would involve breach of contract.
Contract law is a large and complex area of the law. You can find a summary of the main principles of contract law by visiting the Wikipedia page titled English contract law.
Landmark Cases in the Law of Contract was created in 2008.
looking at the case law and other authorities do you think that contract law today is based on yhe three principles of privity of contarct,sanctity of contarct andfreedom of contract
No. The contract is bound by the law that existed and was known to the parties at the time the contract was drawn up and signed.
Statute law takes precedence over the others. Where it doesn't conflict with the written laws, contract law will be next. Common law is only relied on as a last resort.
The contract will say which law is in effect but cannot be canged after it has been signed so will be the law that was there when it was signed.
Whether your sister-in-law should clean for you is entirely a matter of circumstance and opinion. There is no general answer.