Taxable event: occurrence fixes liability while quantification and collection may be postponed for administrative and procedural reasons. A taxable event is the occurrence that fixes liability to tax, although quantification and collection may be postponed for administrative convenience. The framework separates three stages: declaration of liability (who and what is taxable), assessment (particularising the exact sum payable), and recovery (methods to collect unpaid tax). Administrative deferral of assessment or recovery does not alter the moment liability arises.