It is the obligation on the party who seeks judgment in their favour to establish their case by adducing sufficient supporting evidence to satisfy the relevant court’s standard of proof. In civil matters in Australia, the person who has the ‘burden’ or ‘onus’ of proof must prove their case to the requisite standard, being the ‘balance of probabilities’. This means that in order for a plaintiff to be successful in a matter involving a breach of contract, the onus is on them to establish on the evidence before the Court that their version of events resulting in the breach are more likely to have occurred than not.
There are specific circumstances whereby the burden ‘shifts’ from a plaintiff to a defendant. An example of this arises in the context of contract law and the duty of a plaintiff to mitigate their loss. A plaintiff is under a duty to mitigate their loss that arises from a breach a contract, meaning that they must take all reasonable steps to reduce their loss. In this situation the onus shifts from the plaintiff to the defendant and it is up to the defendant to prove of the balance of probabilities that the plaintiff has not taken reasonable steps to reduce their loss. In a situation where the defendant is able to prove that the plaintiff has not mitigated their loss, the award of damages may be reduced by the Court.