Johnny purchases a house, doesn't want furniture left behind. He signs Tuesday, changes mind Thursday, calls agent to add furniture to contract. What is this?

An option is a separate contract giving one party the right but not the obligation to buy at a set price within a stated period; it does not describe adding new terms to an already-signed purchase contract.

Novation substitutes a new contract or party for an existing one, extinguishing the original obligation. Adding a furniture clause does not replace or discharge the existing purchase agreement.

An amendment modifies terms that are already part of an existing contract (e.g., changing the price or closing date). Because the original contract said nothing about furniture, the change is properly characterized as an addition (addendum) rather than a modification.