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.
Obligations are divided into contract, quasi-contract and tort. The Roman law attempted to add a fourth class, the quasi-delict; but the rights which are grouped under this class can be distributed among other headings. Contract is the form of obligation which arises out of the agreement of the parties. They are free in advance to enter into it or not, as they may choose. The obligation which is thus created may be affirmative or negative or both, in accordance with the terms of the agreement. Quasi-contract is a form of obligation which does not depend upon the consent of the obligor and which is frequently imposed upon him in defiance of his will. It binds him to affirmative action in the form of making restitution and of restoring an unjust enrichment which the obligor has received to the party who is lawfully entitled thereto. Tort is an obligation which is entered into by reason of the obligor's wrongful act or default in violating a duty which is imposed upon him by law without regard to his assent, the violation of which duty inflicts an injury upon the obligee. The original duty at our law and at Roman law is to abstain from the wrongful act. Neither system of law imposes affirmative duties, the violation of which amounts to a tort or delict. It may be doubted, however, whether this is an essential feature of tort action. Both systems of law impose cer-tain affirmative duties; and a system of law might be imagined in which a breach of an affirmative duty might give rise to a tort action.