Bar-Mordecai v Hillston

The High Court of Australia considered an appeal concerning the enforceability of a settlement agreement reached between the parties, Mr. Bar-Mordecai and Mr. Hillston, in earlier proceedings. The dispute centred on whether the settlement agreement, which was intended to resolve a complex commercial dispute, was valid and binding, or whether it had been vitiated by a fundamental mistake.

The primary legal issue before the High Court was whether the parties had entered into the settlement agreement under a common mistake as to a fundamental aspect of the contract, thereby rendering it void. Specifically, the court had to determine if the mistake related to the existence of a debt that was the subject of the underlying dispute, and if so, whether that mistake was so fundamental as to vitiate the agreement.

McHugh and Heydon JJ, in their joint judgment, held that for a contract to be voidable due to common mistake, the mistake must be about the existence of the very subject matter of the contract. They found that the parties' mistake, if any, was not about the existence of the debt itself, but rather about the legal enforceability of that debt. This distinction was crucial, as a mistake concerning the legal rights and obligations arising from a contract, rather than the existence of the subject matter, does not typically render a contract void. The court applied the principles established in *Bell v Lever Bros Ltd* and *Great Peace Shipping Ltd v Tsavliris Salvage (International) Ltd*, emphasizing that the mistake must be fundamental to the identity of the subject matter.

The High Court allowed the appeal, finding that the settlement agreement was not voidable due to common mistake. Consequently, the court ordered that the settlement agreement be upheld and enforced.