But this principle of equivalency is not the only principle to be drawn even from the form of contracts, without considering their subject-matter, and of course it is not offered as such in Mr. Langdell’s work.

Another very clear one is found in contracts for the sale or lease of a thing, and the like.  Here the qualities or characteristics which the owner promises that the thing furnished shall possess, go to describe the thing which the buyer promises to accept.  If any of the promised traits are wanting in the thing tendered, the buyer may refuse to accept, not merely on the ground that he has not [336] been offered the equivalent for keeping his promise, but also on the ground that he never promised to accept what is offered him. 1 It has been seen that, where the contract contains a statement touching the condition of the thing at an earlier time than the moment for its acceptance, the past condition may not always be held to enter into the description of the thing to be accepted.  But no such escape is possible here.  Nevertheless there are limits to the right of refusal even in the present class of cases.  If the thing promised is specific, the preponderance of that part of the description which identifies the object by reference to the senses is sometimes strikingly illustrated.  One case has gone so far as to hold that performance of an executory contract to purchase a specific thing cannot be refused because it fails to come up to the warranted quality. 2

Another principle of dependency to be drawn from the form of the contract itself is, that performance of the promise on one side may be manifestly intended to furnish the means for performing the promise on the other.  If a tenant should promise to make repairs, and the landlord should promise to furnish him wood for the purpose, it is believed that at the present day, whatever may have been the old decisions, the tenant’s duty to repair would be dependent upon the landlord’s furnishing the material when required. 3

[337] Another case of a somewhat exceptional kind is where a party to a bilateral contract agrees to do certain things and to give security for his performance.  Here it is manifest good-sense to hold giving the security a condition of performance on the other side, if it be possible.  For the requirement of security shows that the party requiring it was not content to rely on the simple promise of the other side, which he would be compelled to do if he had to perform before the security was given, and thus the very object of requiring it would be defeated. 1