overlook consideration of the matter.40 Kleinschmidt argues that §397 is permissive rather than prescriptive: it allows for contractual renunciation,­ but does not forbid a unilateral renunciation. He further argues that, though §311(1) seems as a general principle to require a contractual route for the creation and variation of obligations, if the purpose of that provi­ sion is considered (it being designed to encapsulate freedom of contract), then it is consistent with that purpose to recognise unilateral renunci­ ations, if that is the form which the renouncing party wishes to give the renunciation. In support of this argument, Kleinschmidt points out that under §423, an agreement between a creditor and one of a number of joint debtors can have the effect of extinguishing the whole debt, the renunci­ ation of the debt taking effect against the other debtors unilaterally, even without their consent. If then renunciation of contractual debts can effec­ tively occur unilaterally so far as co-debtors are concerned, it cannot be the case that there is any theoretical objection to such renunciations in favour of a sole debtor.

Though Kleinschmidt’s position that unilateral renunciations are pres­ ently permissible under the existing provisions of the BGB has not per­ suaded all commentators,41 most have recognised that the case he has put for recognising such renunciations is a convincing one. If German courts are in effect permitting such unilateral renunciations, it would surely be more honest for the legal system to recognise them for what they are and to cease to force essentially unilateral acts into a bilateral contractual model.

5.  Forbearance, promissory estoppel and personal bar

Having considered renunciations of rights which are recognised as valid contractual or promissory alterations, it is necessary also to say something about those renunciations which are given effect as a result of a party’s behaviour preventing it from acting at odds with consent which it is deemed to have given to an undertaking. The idea of using promise to explain this result has been influential in a number of legal systems, but it has not been the only explanation for the basis of liability. Alternatively, it can be argued either that it is the principle of good faith

40See Kleinschmidt, Der Verzicht im Schuldrecht. Kleinschmidt’s argument has generated support from the following (among others): Zimmermann, ‘Europa und das römische Recht’, 243, 270; Schulze, in Anwaltkommentar zum BGB, §§145–147, n. 15; Stoll, ‘Review of Der Verzicht im Schuldrecht’; Kramer, Münchener Kommentar, ‘Einleitung’ n. 55.

41Some feel that his argument stretches the plain meaning of the text of the BGB.