THE LAW OF CONTRACTS
Roman law did not have a general law of contract. For a contract to be enforceable, it had to fall within one of the types specified by the law. This contrasts with modern law, in which any seriously intended agreement is in principle enforceable: as Stair says for Scots law, “every paction produceth action” (Stair, Institutions 1,10,7).
A modern textbook on contract law will be mostly made up of consideration of general principles, with specific types of contract (such as sale or hire) being considered separately or not at all. For the Romans, the priority was reversed. In the Roman sources, the emphasis was on the specific contracts. There was very little recognition of common principles applying to contracts generally, although there were some rules of general application. For example, in the classical law, someone who had been induced to enter into a contract by duress or fraud had a defence to any attempt to enforce that contract.The Institutional Scheme divided contracts into four categories, depending on how they were constituted: obligations arising by conduct; obligations arising by words; obligations arising by writing; and obligations arising by agreement. It was not enough that there was an agreement. The parties also had to comply with the specific requirements for the contract in question before a valid contract could be said to have been constituted.