What doctrine allows a person to argue that a lack of understanding accompanied their signature on a contract?

The doctrine that allows a person to argue that a lack of understanding accompanied their signature on a contract is known as "Non est Factum." This legal principle provides a way for a person to contest the validity of a contract if they were misled about the nature of what they were signing, or if they were unaware of the implications of the document due to factors such as a mental impairment or lack of understanding. Essentially, it protects individuals who may have signed a contract under circumstances where they did not fully comprehend what they were agreeing to, thus invalidating their consent to the contractual terms.

In contrast, the other options like Innocent Misrepresentation and Fraudulent Misrepresentation relate to different circumstances where a misleading statement induces someone into a contract, but do not address the issue of understanding or knowledge at the time of signing. Quantum Meruit pertains to a claim for payment for services rendered when no formal contract exists, which is unrelated to the concept of signature understanding. Therefore, Non est Factum is the appropriate doctrine for addressing a lack of understanding regarding a contract.