Yes, it is possible for both parties to be called as promisers in a valid contract. In contract law, a promiser is a party who makes a promise to perform a certain action or provide a certain service, while a promisee is the party to whom the promise is made. In most contracts, there is usually one promiser and one promisee. However, there are certain situations where both parties can be considered promisers.

Mutual promises:
In a bilateral contract, both parties make mutual promises to each other. This means that each party is both a promiser and a promisee. For example, in a contract for the sale of goods, the buyer promises to pay the agreed-upon price, while the seller promises to deliver the goods. Both parties are promisers because they are making promises to each other.

Conditional promises:
In some contracts, the promises made by each party are conditioned upon the other party's performance. This means that both parties are promisers, as their promises are dependent on each other. For example, in a contract for the construction of a house, the owner promises to make progress payments to the contractor as the work is completed, while the contractor promises to complete the construction according to the agreed-upon specifications. Here, both parties are promisers because their promises are contingent on the other party's performance.

Joint obligations:
In certain contracts, both parties may have joint obligations to perform a certain action. In this case, both parties are considered promisers. For instance, in a partnership agreement, all partners have joint obligations to contribute capital, share profits, and make decisions. Each partner is a promiser because they have obligations to the partnership and to the other partners.

Conclusion:
In summary, it is possible for both parties to be called as promisers in a valid contract. This can occur in situations where there are mutual promises, conditional promises, or joint obligations. It is important to understand the roles of promisers and promisees in a contract to ensure clarity and enforceability of the agreement.