According to Article 32 of the Contract Law, "If the parties conclude a contract in the form of a contract, the contract is established when both parties sign or seal it", it can be seen that a written contract that requires both parties to sign or seal it in principle can be established. Then, in jurisprudence, we always think that a contract is established when both parties agree on their intentions, that is, as long as one party makes an offer, the other party makes a promise. At this point, the contract was actually established. Article 25 of the Contract Law also confirms this theory. At the same time, Article 37 stipulates that "if a contract is concluded in the form of a contract including a letter of confirmation, one party has fulfilled its main obligations and the other party accepts it before signing or sealing, the contract is established." So how to determine the validity of this kind of contract? It should be considered from the following angles:

1. Only one party signs or seals the contract. If one party (whether signed or sealed) fulfills the main obligations of the contract and the other party accepts it, the contract is established, regardless of whether the recipient has also fulfilled the corresponding obligations;

Only one party signs or seals the contract. If one party (whether the signatory or the seal party) performs the main obligations of the contract, but it is not accepted by the other party, the contract is not established;

3, only one party signed or sealed the contract, but both parties failed to fulfill the main obligations of the contract, the contract is not established;

4. If both parties fail to sign or seal the contract, one party has fulfilled the main obligations of the contract and the other party has accepted it, and the contract is established, regardless of whether the recipient has also fulfilled the corresponding obligations;

5. Neither party has signed or sealed the contract, and if one party has fulfilled the main obligations of the contract but has not been accepted by the other party, the contract is not established;

6. Neither party has signed or sealed the contract, and neither party has fulfilled the main obligations of the contract, so the contract is not established.