This section is from the book "The Law Of Contracts", by William Herbert Page. Also available from Amazon: Commercial Contracts: A Practical Guide to Deals, Contracts, Agreements and Promises.
The modern theory that contract is an agreement enforceable at law has disarranged common law classifications based on the form of action. However, since the common-law classification went back to the beginning of the common law itself, it survives to this day, though the original reason for its existence has long since vanished. The simple contract, though the last to be developed, is now looked upon at modern law as the contract par excellence. It is the representative type of contract at modern law, and possesses all the elements requisite therefor, since it is an agreement which by reason of its consideration, the law will enforce. Whether the simple contract is express or implied makes no difference except as to the evidence by which it is to be proved, as long as it is a genuine agreement. Contracts under seal may now be regarded genuine contracts, since they are agreements which, by reason of their form, are enforceable at law. They do not possess the same elements as simple contracts; for they require form, which simple contracts do not; and do not require consideration, which simple contracts do; but they are included under the definition of contract. By reason of the abolition of private seals in many jurisdictions, and the requirement of a consideration even in contracts under seal, this class of contracts has lost its original importance. A discussion of the peculiarities of sealed contracts is for this reason reserved until after the elements of simple contracts have been treated.1
4 See Sec. 566.
1 See ch. XXXIX.