the underlying principle is that people are free to hold what they have. An obligation to redress an enrichment is imposed only in carefully regulated circumstances. In particular, rules ensure that one person cannot force another to pay for an enrichment resulting from a disadvantage to which the first person has consented freely and without error.19 That would be an unwarranted infringement of freedom. Rules also ensure that those who are enriched by receiving a non-transferable benefit without their consent (such as receiving an unwanted service) are not compelled to reverse that enrichment by paying for its value, since this would in substance require the recipient of an enrichment to perform a bargain not voluntarily concluded. If they are liable at all, their liability is therefore not allowed to exceed any sum which they would have spent in any case in order to enjoy the benefit which they have unwittingly or unwillingly received.20

Property

14.Limited scope for party autonomy. The principle of party autonomy has to be considerably modified in property law. Because proprietary rights affect third parties generally, the parties to a transaction are not free to create their own basic rules as they wish. They cannot, for example, define for themselves basic concepts like “possession”. Nor are they free to modify the basic rules on how ownership can be acquired, transferred or lost. Under the DCFR they cannot even agree to an effective contractual prohibition on alienation.21 The free alienability of goods is important not only to the persons concerned but also to society at large. One type of freedom is restricted in order to promote another – and efficiency.

15.Recognition and enhancement of freedom in some respects. Within the essential limits just noted, the principle of party autonomy is reflected in Book VIII. It can be seen in the rule that the parties to a

19VII. – 2:101(1)(b).

20VII. – 5:102(2).

21VIII. – 1:301.

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