A new legal idea is usually treated in law as analogous to the earlier ideas with which the law is familiar, and as being as nearly identical with such earlier legal ideas as is possible. The king's courts, when they began to develop assumpsit as a means of enforcing simple executory promises, were familiar with the executory promise under seal; and at the outset they treated the new informal contract as analogous to the older formal contract. The sealed contract was regarded as necessarily complete upon its face. No covenants could be introduced into the sealed contract by construction. The new informal contract was treated, at first, in the same way. After assumpsit became established as the action by which express executory contracts, not under seal, could be enforced, the courts at first insisted upon an express promise, and refused to enforce a genuine agreement of the parties which- was reached by acts and conduct.1 It was assumed that a request to another to perform work and labor imposes no obligation upon the party making such request in the absence of an express promise to pay therefor.2 A request to become surety for a third person carried with it no obligation to exonerate such surety in the absence of an express promise so to do;3 but on the other hand assumpsit would lie on such an express promise, although it was made after such liability as surety had been incurred.4 An oral promise to submit to an award imposed no liability to perform the award in the absence of an express promise so to do.5 An award under the hands and seals of arbitrators was not within the original statute of limitations since it was not a specialty and it was not a lending or contract.6 In other words, the new kind of contract was treated at the outset as informal in one sense, since it did not owe its validity to its form alone; but on the other hand, it was treated as a formal contract in the sense that all the terms thereof had to be set forth in express words, and that no terms could be added thereto by construction.

4 In Rolle's Abridgment, 1 et seq., Action sur case, the actions "sur assumpsit" are separated from tort actions. See (m) et seq., pp. 6 et seq.

5 See Sec. 25.

6 See Sec. 18, 47, 1493 et seq.