1. If the debtor is in delay in delivering a determinate thing which subsequently got lost due to fortuitous event, the debtor shall be liable for the loss.
2. Generic thing never perishes.
3. In case a passenger is injured due to the negligence of the taxi driver, the passenger may sue the taxi driver based on quasi- delict. He may include the taxi operator in the suit based on the employer's solidary liability for the acts of its employee.
4. In case a passenger is injured due to the negligence of the taxi driver, the passenger may sue the taxi operator based on breach of contract of carriage. He may not include the taxi driver since a contract of carriage is only between the taxi operator and the passenger.
5. While a natural obligation cannot be enforced, if voluntarily fulfilled, recovery of what has been delivered or performed can no longer be made.
6. The diligence required of common carriers is extraordinary diligence, which is greater than the diligence of a good father of a family.
7. While solidary debtors may be compelled to pay the share of an insolvent co-debtor, joint debtors may not be compelled to do so.
8. In alternative obligations, the person entitled to choose cannot choose the things lost due to fortuitous event or due to the fault of the one entitled to choose.
9. The obligation to deliver determinate things includes the obligation to deliver the accessions and accessories even it not mentioned in the agreement.
10. In obligations with a period, the debtor loses the benefit to make use of the period if he fails to furnish the security which he has promised.
11. In obligations with a penal clause, the payment of penalty does not require proof of actual damages.
12. In facultative obligations, the choice to substitute always belongs to the debtor.