1. See if the impostor has the authority to act as an agent or seems to act as an agent, or whether it is ratified afterwards, if the ratification is valid;
2. If there is no agency authority or the agency is obvious, the IOU is only valid for the actual borrower. If it is proved that the loan is used for husband and wife's life or production and operation, it may also belong to husband and wife's debt. Husband and wife are jointly and severally liable.
If one of the spouses has no power of attorney, exceeds the power of attorney or concludes a contract in the name of the principal after the termination of the power of attorney, the contract is invalid under any of the following circumstances:
1. One party enters into a contract by means of fraud or coercion, which harms the national interests;
2, malicious collusion, damage the interests of the state, the collective or the third party;
3. Covering up illegal purposes in a legal form;
4, damage the public interests;
5. Violation of mandatory provisions of laws and administrative regulations.
To sum up, the IOU signed by one spouse is valid, but it can only be signed on behalf of the other spouse if authorized by the other spouse. Debts jointly signed by husband and wife or ratified by one of them with the same meaning afterwards. Belonging to the same debt of husband and wife, both husband and wife have the obligation to pay off.
Legal basis:
Article 1064 of the Civil Code of People's Republic of China (PRC)
The debts incurred by both husband and wife after the same signature or ratification by one party, and the debts incurred by one party in his own name for the daily needs of the family during the marriage relationship, belong to the same debt of husband and wife.
Debts incurred by one spouse in his own name during the marriage relationship that exceed the needs of family daily life are not joint debts of husband and wife; However, the creditor can prove that the debt is used for the husband and wife's life, production and operation, or based on the same meaning of both husband and wife.