In the chapters that follow, first the law of contract, then unjustified enrichment, and finally the law of delict will be dealt with.

The discussion of contract commences with the special contracts before it focuses on general doctrines. This progression from the concrete to the more abstract and general would appear to accord best with the way the Roman lawyers developed their law of contractual obligations.

Fundamental, however, to the subject matter of this book is the Roman concept of an obligation and it appears to be apposite, therefore, first to consider three of its most important implications (Chapter 2). We shall then proceed to discuss the stipulation, prototype of a contract verbis and cornerstone of the Roman contractual system. Two particularly important types of transaction (conventional penalties and suretyship) which had to be concluded by way of a stipulation will be examined next {Chapters 4 and 5). The following two chapters are devoted to the four real contracts (mutuum, commodatum, depositum, pignus), the next eight to the four consensual contracts (emptio venditio, locatio conductio, mandatum and societas).^[157] Though not a contract, negotiorum gestio will be dealt with, for the sake of convenience, as an appendage to mandatum. Donation will be discussed last (Chapter 16); it was not a contract in classical Roman law, but became one in post-classical times. The chapter on pacta and innominate real contracts will take us into the general part of our study of the law of contract, for it is here that we find the doctrinal bridge towards the modern general law of contract. In the subsequent chapters consideration will therefore be given to the most important problem areas affecting every type of contract: how does it come into existence and what is it based upon; what are the effects of error, of metus and of dolus on the contractual relationship between the parties; what are the principles governing the interpretation of contracts; under which circumstances are contracts invalid and how can the obligations arising therefrom be terminated; which provisions may the parties include in their contract (conditions and time clauses will be dealt with as an example of two particularly important examples); and what are the consequences of a breach of contract. The law of unjustified enrichment forms the subject of Chapter 26; together with negotiorum gestio (Chapter 14), it is the only "quasi-contract" considered in some detail.

arising from a contract of sale. For a thorough analysis along these lines, cf. Ralf Michael Thilo. Der Codex accepti et expensi im Romischen Recht (1980"). pp. 42 sqq.. 79 sqq. (on the Roman bookkeeping and accounting system), pp. 162 sqq. (on the codex accepti et expensi), pp. 276 sqq. (on the contract litteris); c{. further, for example, Savigny, Vermischte Schriften. vol. I (1850), pp. 205 sqq.; De Zulueta, Gaius II, pp. 163 sqq.; Thielmann, Privatauktion. pp. 110 sqq.; 196 sqq.; Watson, Obligations, pp. 18 sqq.; Pierrejouanique, "Le codex accepti et expensi chez Ciceron", (1968) 46 RH 5 sqq.; M.W.E. Glautier, "A Study in the development of Accounting in Roman Times", (1972) 19 RIDA 310 sqq.; Honsell/Mayer- Maly/Selb, pp. 251 sqq.