An acceptance must be expressed in some usual and reasonable manner, unless the proposal prescribes the manner in which it is to be accepted… In Anson’s Law of Contract it has been stated that Acceptance means in general communicated acceptance. The learned Author says at page 44: “We have seen that the acceptance of an offer requires more than a tacit formation of intention. There must be some overt act or speech to give evidence of that intention. But English law stipulates in addition that acceptance is not complete unless and until it is communicated to the offeror. In the words of Lindley LJ: 'Unquestionably, as a general proposition when an offer is made, it is necessary in order to make a binding contract, not only that it should be accepted, but that the acceptance should be notified.' Since, however, notification is for the benefit of the offeror, he may expressly or impliedly waive this requirement and agree that an uncommunicated acceptance will suffice. Thus, acceptance may in circumstances be held to have been made even though it has not yet come to the notice of the offeror. In such a case, two things are necessary. There must be an express or implied intimation from the offeror that a particular mode of acceptance will suffice. And some overt act must be done by the offeree which is evidence of an intention to accept, and which conforms to the mode of acceptance indicated by the offeror. These requirements may be summed up in the proposition that an offer is accepted when acceptance is made in a manner prescribed or indicated by the offeror.” 

( Bangladesh Moktijoddah Kalyan Trust rep. by MD Vs. Kamal Trading Agency & others. 1997, 26 CLC (AD) [491] )  

Acceptance is an expression signifying consent to the terms of an offer. In other words, to agree to the terms and conditions of an offer contract. The validity of an acceptance is governed by four principal rules. (1) it must take place while the offer is still in force, i.e. before it has lapsed or been revoked. (2) it must be on the same terms as the offer. An acceptance made subject to any variation is treated as a counteroffer. (3) it must be unconditional, thus an acceptance subject to contract is not a valid acceptance. (4) it must be communicated to the offeror. 

( Hyde Vs. Wrench (1840) 3 Beav 334; Carlill Vs. Carbolic Smoke Ball Co. (1983) 1 QB 256 )

As soon as the acceptance is posted or sent by telegram, the acceptance is complete against the proposer and the contract is concluded. A person posting a letter of acceptance is not answerable for casualties occurring at the post office- Consequently, the contract was complete and binding on the proposer immediately after the acceptance was posted and it was not revoked. It is rather the liability of the acceptor that would start only after the Acceptance comes to the knowledge of the proposer. 

( PLD 1984 Lahore 430 )

The communication of a counter offer does not amount to the acceptance of a proposal or an offer made by the other party. 

( Abdul Aziz Vs. The Rent Controller, PLD 1958 (Kar) 278 )

See, Sections 4, 7, 8 of the Contract Act, 1872; Sections 35, 112, of the Transfer of Property Act, 1882; Section 17, the Bill of Exchange Act, 1882.