Final answer:
To avoid a contract for the car sale due to mental incapacity, a party must prove inability to understand the transaction when the contract was made, often by showing lack of contractual capacity through evidence of a mental condition.
Step-by-step explanation:
In order to avoid a contract for the sale of a car based on mental incapacity, a party must prove that they were not able to understand the nature and consequences of the transaction at the time the contract was made. This may involve demonstrating that the person did not have the ability to understand the terms of the contract, the nature of the car being sold, or the obligations and rights that come with entering into a contract. Often, this would require medical evidence or testimony regarding the individual's mental state at the time of the agreement.
In legal terms, the party seeking to void the contract would need to show that they lacked contractual capacity, which is the mental ability to understand the rights and obligations being entered into. Lack of such capacity can stem from a variety of conditions, including but not limited to, severe mental illness, cognitive impairments, or the effects of intoxicating substances.
If a court finds that a contract was entered into under these circumstances, it may declare the contract void or voidable at the option of the incapacitated party, thus releasing them from the contractual obligations.