51. When a contract consists of reciprocal promises to be simultaneously performed, no promisor need perform his promise unless the promisee is ready and willing to perform his reciprocal promise.  
Illustrations  
(a) A and B contract that A shall deliver goods to B to be paid for by B on delivery. 
 A need not deliver the goods, unless B is ready and willing to pay for the goods on delivery.  
B need not pay for the goods, unless A is ready and willing to deliver them on payment.  
(b) A and B contract that A shall deliver goods to B at a price to be paid by installments, the first installment to be paid on delivery.  
A need not deliver, unless B is ready and willing to pay the first installment on delivery.  
B need not pay the first installment, unless A is ready and willing to deliver the goods on payment of the first installment.  
Order of performance of reciprocal promises  
52. Where the order in which reciprocal promises are to be performed is expressly fixed by the contract, they shall be performed in that order; and, where the order is not expressly fixed by the contract, they shall be performed in that order which the nature of the transaction requires.  
Illustrations  
(a) A and B contract that A shall build a house for B at a fixed price. A's promise to build the house must be performed before B's promise to pay for it.  
(b) A and B contract that A shall make over his stock-in-trade to B at a fixed price, and B promises to give security for the payment of the money. A's promise need not be performed until the security is given, for the nature of the transaction requires that A should have security before he delivers up his stock.  
Liability of party preventing event on which the contract is to take effect  
53. When a contract contains reciprocal promises, and one party to the contract prevents the other from performing his promise, the contract becomes voidable at the option of the party so prevented; and he is entitled to compensation from the other party for any loss which he may sustain in consequence of the non-performance of the contract.  
Illustrations  
A and B contract that B shall execute certain work for A for a thousand Taka. B is ready and willing to execute the work accordingly, but A prevents him from doing so. The contract is voidable at the option of B; and, if he elects to rescind it, he is entitled to recover from A compensation for any loss which he has incurred by its non-performance. 
 Effect of default as to that promise which should be first performed, in contract consisting of reciprocal promises  
54. When a contract consists of reciprocal promises, such that one of them cannot be performed, or that its performance cannot be claimed till the other has been performed, and the promisor of the promise last mentioned fails to perform it, such promisor cannot claim the performance of the reciprocal promise, and must make compensation to the other party to the contract for any loss which such other party may sustain by the non-performance of the contract.  
Illustrations  
(a) A hires B's ship to take in and convey, from Chittagong to the Mauritius, a cargo to be provided by A, B receiving a certain freight for its conveyance. A does not provide any cargo for the ship. A cannot claim the performance of B's promise, and must make compensation to B for the loss which B sustains by the non-performance of the contract.  
(b) A contracts with B to execute certain builder's work for a fixed price, B supplying the scaffolding and timber necessary for the work. B refuses to furnish any scaffolding or timber, and the work cannot be executed. A need not execute the work, and B is bound to make compensation to A for any loss caused to him by the non-performance of the contract.  
(c) A contracts with B to deliver to him, at a specified price, certain merchandise on board a ship which cannot arrive for a month, and B engages to pay for the merchandise within a week from the date of the contract. B does not pay within the week. A's promise to deliver need not be performed, and B must make compensation.  
(d) A promises B to sell him one hundred bales of merchandise, to be delivered next day, and B promises A to pay for them within a month. A does not deliver according to his promise. B's promise to pay need not be performed, and A must make compensation.  
Effect of failure to perform at fixed time, in contract in which time is essential  
55. When a party to a contract promises to do a certain thing at or before a specified time, or certain things at or before a specified times, and fails to do any such thing at or before the specified time, the contract, or so much of it as has not been performed, becomes voidable at the option of the promisee, if the intention of the parties was that time should be of the essence of the contract.  
Effect of such failure when time is not essential  
If it was not the intention of the parties that time should be of the essence of the contract, the contract does not become voidable by the failure to do such thing at or before the specified time; but the promisee is entitled to compensation from the promisor for any loss occasioned to him by such failure.  
Effect of acceptance of performance at time other than that agreed upon  
If, in case of a contract voidable on account of the promisor's failure to perform his promise at the time agreed, the promisee accepts performance of such promise at any time other than that agreed, the promisee cannot claim compensation for any loss occasioned by the non-performance of the promise at the time agreed, unless, at the time of such acceptance he gives notice to the promisor of his intention to do so.