The Concept of Non-Contractual Obligations

parties are free in principle to agree on whatever they choose. Moreover, and 
perhaps more importantly, they are protected against unwanted quasi-contractual 
obligations imposed by the law. As a matter of principle, obligations to perform 
require the consent of the debtor. Hence, contractual obligations must not be 
enforced on parties that did not agree.
93
Of course, nobody doubts, as a matter of 
principle, that the law of unjustified enrichment must not violate this principle by 
imposing quasi-contractual obligations in situations where contract law refuses to 
acknowledge a binding contract. Yet this is precisely what may be the result of an 
application of the 
condictio ob rem
, especially in cases where services have been 
rendered without a contractual basis. 
The problematic cases concern disappointed expectations with regard to the 
future behaviour of the other party, often within close social relations. Typically, 
one person renders services to an elderly recipient, or improves the recipient‟s 
property. Often this is done in consideration of the recipient‟s promise to be 
benefited in his or her last will.
94
Such agreements are usually void for a lack of 
form, and the parties are often perfectly aware of this. Nevertheless, it may be 
unfair to leave the disappointed party without redress. Similar problems arise in 
cases where not even an agreement of this kind can be found. Often, the parties 
have been motivated more by compassion and a sense of moral duty than by 
rational economic considerations. Nevertheless, there may have been a tacit mutual 
89
See above at fn 84. 
90
Cf 
B Windscheid
, Lehrbuch des Pandektenrechts (7th edn 1891) vol II, 207 f, 543 ff (§§ 321, 
424 f).
 
91
MüKo/
Lieb
(fn 60) § 818, [200] f: on the one hand, Lieb postulates a „Willenseinigung … des 
Inhalts …, dass der Empfänger die Leistung nur im Hinblick auf die von ihm erwartete 
Gegenleistung … erhält‟ ([201]), yet the author insists: „Diese Abrede darf … nicht 
rechtsgeschäftlich ausgebildet sein‟ ([200]). 
92
C Wendehorst
, Ungerechtfertigte Bereicherung, in: R Schulze/C von Bar/H Schulte-Nölke (eds), 
Der akademische Entwurf für einen Gemeinsamen Referenzrahmen: Kontroversen und Perspektiven 
(2008) 215, 243 f; cf also 
S Hedley
, Unjust Enrichment (1995) 54 Cambridge Law Journal (CLJ) 
578–599, 592 f; 
id
(fn 74) 74. 
93
Hedley
has rightly emphasised, in this context, that it is of course for contract law to decide what 
counts as an agreement giving rise to contractual liability: Restitution (fn 74) 58 ff. It would be a 
fiction to assume that all contractual obligations are based on the parties‟ explicit consent. Contracts 
likewise protect the reasonable reliance in contractual behaviour of others. 
94
CA Mons (22 March 1989) [1989] Revue du notariat belge
 
534 ff (awarding FF 250,000); BGHZ 
44, 321 ff (29 November 1965); BGHZ 108, 256 ff (12 July 1989); OGH SZ 36, 83 ff, no 30 
(26 February 1963).
 

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18 
understanding that the services were not rendered for free, and that some reward 
would be received, therefore, from the inheritance. And often there is even no such 
understanding, but only the hope of being favourably considered in the recipient‟s 
last will. 
In such cases it is difficult to find out in retrospect what kind of agreement 
existed between the parties. However, whereas the law may well protect justified 
reliance on a contractual agreement even if the agreement turns out to be void, it 
should not create incentives for legacy hunting. Mere motives must be immaterial.
95
Nevertheless, if there was mutual agreement about services rendered for 
economically valuable reward, or if there was only an understanding that the 
services were not rendered for free, these cases are probably best discussed within 
the framework of contract law. A person who freely accepts services or other 
benefits cannot later claim that there was no contractual agreement
96
and, if the 
agreement was void, the normal contractual remedies should apply. Indeed, the 
value of services received must often in such cases be determined on the basis of 
the parties‟ agreement as the parties were aware of the beneficiary‟s inability to pay 
the market price for the services rendered. Courts tend to take this into 
consideration when evaluating the value of the services.
97
It follows that such 
claims must be discussed on the basis of contract law policy even if such 
agreements are void.
98
Indeed, if the parties are aware of their agreement being 
unenforceable, it may often be presumed that there is a tacit agreement that the 
recipient should return the value of the benefit received
99
when disappointing the 
other party‟s expectations.
100
True, such a presumption may amount to a fiction and 
such an approach parallels the old quasi-contract theory in that the claims are 
treated not as remedies but rather as primary contractual claims for performance. 
Yet, in such cases this approach is normatively adequate: the fiction of a tacit 
agreement leads lawyers to ask the relevant questions (namely, what the parties 
would have agreed upon had they addressed the question of their agreement‟s 
voidness) rather than misleading ones (namely, about the defendant‟s abstract 
95
This is agreed even by German supporters of this type of restitution; see