Up to this time, we have been considering only absolute contracts. There are, however, other contracts known as conditional contracts. A conditional contract is one which goes into effect or is determined by the happening or not happening of a certain event. Conditional contracts are divided into three classes, including: (1) Conditions precedent; (2) conditions concurrent; and (3) conditions subsequent. In the case of conditions precedent, the happening of the event must take place before the rights of the promisee arise. In the case of conditions concurrent, the promisee's rights and the happening of the event must take place simultaneously, and in the case of conditions subsequent, the rights of the promisee are determined by the happening of the specified event. There must be mutuality in conditional contracts as in all other contracts, and if the effect of the condition is to destroy the mutuality, the condition fails for want of consideration. Generally, where the contract is conditional the promisor is discharged from liability for the failure of the promisee to fulfill the condition.