It should detail the work, price, when payments will be made. Legality of purpose The agreement must be for a legal purpose.Consideration – Each party must contribute a value to the contract. Legality – The contract's purpose must be lawful and not contrary to public policy to be deemed valid under contract law. The agreement is valid if both parties have signed it. Also, what must be in the agreement is agreement, capacity, consideration, and intention. The definition of a contract in California is a legally binding agreement negotiated between parties. An Irvine business lawyer can help with contracts. California is an atwill employment state. This means that, in California, an employee can be fired for any reason or no reason, with or without notice.