Thesis (LLM)--Stellenbosch University, 2001. / ENGLISH ABSTRACT: On the basis of a comparative analysis of the case law in Germany, England and South Africa dealing with fundamental change of circumstances, it is submitted that the underlying principle of this problem area is the idea of frustration of the contractual purpose (causa finalis). The problem of fundamental change of circumstances is directly connected with basic issues of legal theory such as the dichotomy between legal certainty and substantive justice, the role and limits of interpretation, the concretisation of principles, the adjudication of interests and the problem of value-judgements in the law which are of immediate influence on the understanding of the problem by judges and legal commentators. A broad perspective on the topic is necessarily indicated hereby. The thesis therefore starts off with an account of the role of purpose (causa finalis) in the history of legal philosophy, with a focus on developments in Germany. The continuing relevance of Aristotelian-Thomistic legal thinking is emphasized. The German and English case law dealing with fundamental change of circumstances is analyzed in an analogous manner. An account of the history and development of the doctrines dealing specifically with fundamental change of circumstances is given: the clausuIa rebus sic stantibus of the ius commune, the doctrine of WegJall der Geschaftsgrundlage in Germany and the doctrine of frustration of contract and common mistake in England. The crucial elements of the approach of the courts are restated. The positions of the two most influential German legal authors involved on opposite sides of the debate concerning the doctrine of WegJall der Geschaftsgrundlage are discussed. At the end of the discussion of English case law, the approach of the English courts is compared with that of their German counterparts, providing a basis for the development of the author's understanding of the concept causafinalis. Notwithstanding the fact that South African law does not recognize a doctrine dealing specifically with fundamental change of circumstances, and in spite of dicta to the effect that the English doctrine of frustration of contract is not part of South African law, it is submitted that the doctrine of frustration of contract has nevertheless strongly influenced the South African law of supervening impossibility and supposition, and has arguably become part and parcel of it. Likewise, cases of frustration of the contractual purpose due to a fundamental change of circumstances have been dealt with by means of other doctrinal devices such as common mistake. It is submitted, finally, that the famous and controversial issue of the role of causa in South African law should be reconsidered, since it may contribute to the understanding of the notion of contract, and assist in overcoming the current doctrinal crisis of the theory of contract. / AFRIKAANSE OPSOMMING: Aan die hand van 'n vergelykende analise van die regspraak in Duitsland, Engeland en Suid- Afrika betreffende fundamentele verandering van omstandighede, word ter oorweging gegee dat die beginselonderliggend aan hierdie probleemgebied te vind is in die gedagte van verydeling van die kontraksoogmerk. Die probleem van fundamentele verandering van omstandighede staan in onmiddellike verband met basiese vrae van die regsteorie, onder andere die teenstelling tussen regsekerheid en substantiewe geregtigheid, die rol en perke van uitleg, die konkretisering van beginsels, die opweging van belange en die probleem van waarde-oordele in juridiese verband wat almal inspeel op die hantering van die probleem deur regters en kommentatore. Met die oog hierop is 'n breë invalshoek op die ondersoekveld gebiedend. Die ondersoek neem derhalwe as vertrekpunt 'n oorsig oor die rol van oogmerk (causa finalis) in die geskiedenis van die regsfilosofie met 'n besondere klem op ontwikkelinge in Duitsland. Die deurlopende belang van Aristoteliaans- Thomistiese denkwyses word beklemtoon. Die Duitse en Engelse regspraak betreffende fundamentele verandering van omstandighede word op 'n eenvormige grondslag ontleed. 'n Oorsig van die geskiedenis van leerstukke wat spesifiek verband hou met fundamentele verandering van omstandighede word aangepak, te wete die sg clausuia rebus sic stantibus van die ius commune en die leerstuk van Wegfall der Geschafstgrundlage in Duitsland en die leerstuk van frustration of contract en common mistake in Engeland. Die kemaspek van die benadering van die howe word uitgespel. Die botsende standpunte van twee van die mees invloedryke Duitse denkers in die teoretiese debat bied 'n breë konseptueie raamwerk vir die uiteindelike vergelyking van die Engelse regspraak met die van die Duitse howe en die ontwikkeling van 'n eie standpunt aangaande die begrip causafinalis. Die Suid-Afrikaanse reg erken nie 10 soveel woorde dat veranderende omstandighede as sodanig die bestaan van 'n kontrak raak nie, en in die besonder word die Engelsregtelike leerstuk van frustration of contract in vele regterlike dicta verwerp. Die ondersoek na die Suid-Afrikaanse respraak lei egter tot die gevolgtrekking dat die Suid-Afrikaanse reg aangaande onmoontlikwording van prestasie en die veronderstelling inderdaad in wesenlike opsigte deur die leerstuk van frustration beïnvloed is. Verydeling van die kontraksoogmerk ten gevolge van veranderende omstandighede geniet ook juridiese erkenning deur middel van . ander juridiese meganismes soos die leerstuk van gemeenskaplike dwaling. Die slotsom van die behandeling van die Suid-Afrikaanse reg is dat die berugte en omstrede rol van causa in die Suid-Afrikaanse Kontraktereg herwaardering verg.