The Concept of Non-Contractual Obligations

actio quod metus causa
), reinstating the parties into 
the former legal position, both in procedural and in material law. See 
Zimmermann
(fn 4) 680 f; 
Kaser/Hackl
(fn 41)
 
421 ff; 
Hellwege
(fn 58) 408 ff. 
60
See, for the German 
Saldotheorie
, RGZ 54, 137, 140 f (14 March 1903);
 
M Lieb
in: Münchener 
Kommentar zum BGB (MüKo) (4th edn 2004) § 818, [110] ff, with further references. According to 
this „theory‟, the details of which are disputed, an unjustified enrichment claim unwinding a bilateral 
contract will be granted only to the extent to which the creditor is able to honour the corresponding 
counterclaim. Accordingly, if a car was transferred under a void contract for sale and subsequently 
destroyed in the hands of the buyer, the buyer cannot reclaim the money paid. However, if the price 
was to be paid later, the seller will have to bear the risk, because the contract is void and the 
Saldotheorie
only relates to contracts that have been fulfilled by both parties. What is more, the 
Saldotheorie
arguably leads to unacceptable results where a minor‟s contract is concerned or where 
the seller acted in bad faith. The courts therefore have made exceptions to this theory without, 
however, being able to address the underlying normative questions at all (for references below, 
fn 76, 78; for further critique, 
Schlechtriem
[fn 3] vol I, 404 f). Indeed, from an unjustified 
enrichment perspective, it cannot make a difference whether a contract is void for lack of consent, 
because of one party being a minor, or because of an error on one party‟s side: restitution is owed for 
the bare fact that the contract is void. Now, 
Hellwege
(fn 58) 462 ff has argued convincingly that the 
Saldotheorie
reformulates principles that originally lay at the core of the 
restitutio in integrum
, the 

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12 
synallagmatique renversé
may lead to the unsatisfactory result that the parties find 
themselves factually bound to the originally intended contract despite the contract 
being void. This is highly inappropriate, for example,
 
in cases where minors are 
concerned.
61
All this proves that the law of unjustified enrichment is conceptually 
blind with regard to the fair assignment of risks concerning the benefit received. In 
fact, unjustified enrichment is a purely descriptive category:
62
claims in unjustified 
enrichment are conceptually
 
based on the bare fact that a transfer has been made 
without a legal ground; they do not appropriately distinguish the reasons for which 
the underlying contract is void.
63
Additional problems arise if a legal system provides for different legal 
regimes for unwinding contracts. If some of these regimes are contractual in nature 
whereas others are non-contractual, as often happens to be the case, it is always 
difficult to integrate them doctrinally with one another. Divergent results are a 
natural consequence.
64
Risk may be assigned differently and the object of the 
contract‟s value may be assessed on different terms: subjectively, in accordance 
with the contract, where the remedy is contractual „in nature‟, or objectively, where 
a non-contractual claim for unjustified enrichment is concerned. Typically, non-
contractual remedies apply only if the contract is void and the contract‟s nullity may 
have further consequences for other remedies, such as (contractual) claims for 
ius commune’s
central device for unwinding contracts. Thus, the problems result from the fact that 
the