2. An offer ought to contain a right, if accepted, of compelling the fulfilment of the contract, and this right when not expressed, is always implied.

3. By virtue of his natural liberty, a man may change his will at any time, if it is not to the injury of another; he may, therefore, revoke or recall his offers, at any time before they have been accepted; and, in order to deprive him of this right, the offer must have been accepted on the terms in which it was made. 10 Ves. 438; 2 C. & P. 553.

4. Any qualification of, or departure from those terms, invalidates the offer, unless the same be agreed to by the party who made it. 4 Wheat. R. 225; 3 John. R. 534; 7 John. 470; 6 Wend. 103.

5. When the offer has been made, the party is presumed to be willing to enter into the contract for the time limited, and, if the time be not fixed by the offer, then until it be expressly revoked, or rendered nugatory by a contrary presumption. 6 Wend. 103. See 8 S. & R. 243; 1 Pick. 278; 10 Pick. 326; 12 John. 190; 9 Porter, 605; 1 Bell s Com. 326, 5th ed.; Poth. Vente, n. 32; 1 Bouv. Inst. n. 577, et seq.; and see Acceptance of contracts; Assent; Bid.