1. Time of Determination. Nullity is established ex tunc (from the beginning), while voidability is determined ex nunc (from the moment of voidability onward).
2. Legal Consequences. A null contract has no legal effects, whereas a voidable contract remains valid until it is contested.
3. Assertion. Nullity can be invoked by anyone, whereas voidability must be asserted and proven before a court by the affected party.
4. Circumstances. Nullity is related to fundamental legal rules, while voidability is associated with specific circumstances that affect the free will of the parties.

Understanding nullity and voidability is crucial for properly concluding and fulfilling contracts. The differences between these two concepts determine how contracts that contradict legal rules or arise under certain conditions are treated. The legal consequences of these concepts ensure the protection of the legal interests of the parties and the stability of the legal system.

Exercise:

Identify the type of contract invalidity:

• A entered into a lease contract but was mentally incompetent at the time of conclusion.
• A concluded a contract under a fundamental and excusable mistake.
• A gift contract was concluded with an illicit motive.
• A 17-year-old enters into a vehicle purchase contract.
• A usurious contract.¹⁷³