To succeed in a claim for rectification of an employment contract, a party must establish that there was a common mistake between the contracting parties that does not reflect their true common intention at the time of contracting. A common mistake is a sine qua non for rectification. The mere fact that an employee performs duties different from their contractual designation, or that the employer was aware of the nature of work performed, does not establish the common intention required for rectification. Where positions are advertised in a departmental vacancy circular for specific posts (in this case, Therapist positions), and applicants apply for and accept appointment to those advertised positions, the contractual relationship is determined by the advertised post, not by additional qualifications required or subsequent duties performed. Leave to appeal under section 17(1)(a) of the Superior Courts Act 10 of 2013 requires more than a mere possibility of success or an arguable case - there must be a sound rational basis to conclude there is a reasonable (realistic) prospect of success on appeal.