In a cession in securitatem debiti (security cession), when the secured debt is extinguished or proves to be invalid, the ceded right automatically reverts to the cedent by operation of law without requiring any re-cession by the cessionary. The pledge theory, not the pactum fiduciae theory, applies to cessions in securitatem debiti in South African law, meaning the cedent retains a reversionary interest in the principal debt. This reversionary interest refers to the cedent's interest in the debtor's performance of the principal debt, not to a contractual right against the cessionary for re-cession. For prescription purposes, where rights under a security cession automatically revert to the cedent, the cedent's claim against a party who received payment from the debtor arises when that payment is made, not when the original cession occurred. The automatic reversion principle applies equally whether the secured debt never existed or was subsequently extinguished.