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.