We find that neither of the two decisions have addressed the real issue and cannot be said to be laying down the correct law. The observation in Md. Mohar Ali (supra) stating that an agreement of sale is an unilateral contract is not correct. An unilateral contract refers to a gratuitous promise where only party makes a promise without a return promise. Unilateral contract is explained thus by John D. Calamari & Joseph M. Perillo in The Law of Contracts (4th Edition Para 2-10(a) at pages 64-65):
If A says to B, 'If you walk across the Brooklyn Bridge I will pay you $ 100,' A has made a promise but has not asked. B for a return promise. A has asked B to perform, not a commitment to perform. A has thus made an offer looking to a unilateral contract. B cannot accept this offer by promising to walk the bridge. B must accept, if at all, by performing the act. Because no return promise is requested, at no point is B bound to perform. If B does perform, a contract involving two parties is created, but the contract is classified as unilateral because only one party is ever under an obligation. All agreements of sale are bilateral contracts as promises are made by both -the vendor agreeing to sell and the purchaser agreeing to purchase. On the other hand, the observation in S.M. Gopal Chetty (supra) that unless agreement is signed both by the vendor and purchaser, it is not a valid contract is also not sound. An agreement of sale comes into existence when the vendor agrees to sell and the purchaser agrees to purchase, for an agreed consideration on agreed terms. It can be oral. It can be by exchange of communications which may or may not be signed. It may be by a single document signed by both parties. It can also be by a document in two parts, each party signing one copy and then exchanging the signed copy as a consequence of which the purchaser has the copy signed by the vendor and a vendor has a copy signed by the purchaser. Or it can be by the vendor executing the document and delivering it to the purchaser who accepts it. Section 10 of the Act provides all agreements are contracts if they are made by the free consent by the parties competent to contract, for a lawful consideration and with a lawful object, and are not expressly declared to be void under the provisions . of the Contract Act. The proviso to Section 10 of the Act makes it clear that the section will not apply to contracts which are required to be made in writing or in the presence of witnesses or any law relating to registration of documents. Our attention has not been drawn to any law applicable in Bihar at the relevant time, which requires an agreement of sale to be made in writing or in the presence of witnesses or to be registered. Therefore, even an oral agreement to sell is valid. If so, a written agreement signed by one of the parties, if it evidences such an oral agreement will also be valid. In any agreement of sale, the terms are always negotiated and thereafter reduced in the form of an agreement of sale and signed by both parties or the vendor alone (unless it is by a series of offers and counter-offers by letters or other modes of recognized communication). In India, an agreement of sale signed by the vendor alone and delivered to the purchaser, and accepted by the purchaser, has always been considered to be a valid contract. In the event of breach by the vendor, it can be specifically enforced by the purchaser. There is, however, no practice of purchaser alone signing an agreement of sale.[Para No.7]
The defendant next contended that the agreement of sale in this case (Ex.2) was clearly in a form which required signatures of both vendor and purchaser. It is pointed out that the agreement begins as: "Agreement for sale between Kanika Bose and Parmatma Devi" and not an "Agreement of sale executed by Kanika Bose in favour of Parmatma Devi". Our attention is also drawn to the testimonium clause (the provision at the end of the instrument stating when and by whom it was signed) of the agreement, which reads thus: "In witnesses whereof, the parties hereto have hereunto set and subscribed their respective hands and seals on these presents." It is therefore contended that the agreement specifically contemplated execution by both parties; and as it was not so executed, it was incomplete and unenforceable. We have carefully examined the agreement (Ex.2), a photocopy of which is produced. The testimonium portion in the agreement is in an archaic form which has lost its meaning. Parties no longer 'subscribe their respective hands and seals'. It is true that the format obviously contemplates signature by both parties. But it is clear that the intention 
of the parties was that it should be complete on signature by only the vendor. This is evident from the fact that the document is signed by the vendor and duly witnessed by four witnesses and was delivered to the purchaser. Apart from a separate endorsement made on the date of the agreement itself (7.9.1979) by the vendor acknowledging the receipt of Rs. 2001 as advance, it also contains a second endorsement (which is also duly witnessed) made on 10.10.1979 by the vendor, acknowledging the receipt of a further sum of Rs. 2000 and confirming that the total earnest money received was Rs. 4001. This shows that the purchaser accepted and acted in terms of the agreement which was signed, witnessed and delivered to her as a complete instrument and that she then obtained an endorsement thereon by the vendor, in regard to second payment. If the agreement was not complete, the vendor would not have received a further amount and endorsed an acknowledgement thereon on 10.10.1979. Apart from the above, the evidence of the witnesses also shows that there was a concluded contract. Therefore, even though the draftsman who prepared the agreement might have used a format intended for execution by both vendor and purchaser, the manner in which the parties had proceeded, clearly demonstrated that it was intended to be executed only by the vendor alone. Thus we hold that the agreement of sale (Ext. 2) signed only by the vendor was valid and enforceable by the purchaser. [Para No.8]
