In Slip Knot Investments v Du Toit 2011 4 SA 72 (SCA) the Supreme Court of Appeal had to determine if the material mistake of a contractual party induced by the fraud of an independent third party could sustain a plea of iustus error raised by the mistaken party. The position prior to this decision was uncertain and characterised by inconsistency, mostly occasioned by the application of the iustus error doctrine together with fault. The Supreme Court of Appeal found that in the circumstances the mistaken party was liable, despite the fraud of the third party, on the basis of the reliance theory. The decision is commendable for bringing a measure of certainty to the law of mistake on this point and indicating that the reliance theory (as opposed to the iustus error doctrine) is the appropriate means to resolving such cases. Nevertheless, it is suggested that although the general rule implied by the court's approach is entirely apposite, there may well be exceptional instances where on the basis of relevant policy considerations the reliance theory should not prevail and the mistaken party should be absolved from contractual liability. In this manner reliance, which at first seems reasonable for being induced by the conduct of the contract denier, may upon further reflection be regarded as unreasonable based on the consideration of risk creation at the hand of the contract assertor, for instance. Admitting exceptions in appropriate circumstances would also provide a degree of consonance with earlier case law, where, even if the court's approach was open to theoretical criticism, a court has intuitively felt that liability should not lie.
Third Party Fraud inducing Material Mistake Slip Knot Investments 777 (Pty) Ltd v du Toit 2011 4 SA 72 (SCA)