ISO 9000 and other quality management systems require a documented procedure for dealing with corrective actions and preventive actions. ISO allows them to be dealt with by the same (CPAR) system, but they are different mind sets. Preventive action is reading the manual before you open the box, corrective action is looking at the manual when there is a problem. Routine maintenance for your car is preventive, taking it to the shop when there is an ominous rattle is corrective.
A columnist for the American Society for Quality explains it this way:
On closer reading, however, section 8.5.2 says corrective action eliminates the cause of nonconformities to prevent recurrence, and section 8.5.3 says preventive action determines and eliminates the causes of potential nonconformities … to prevent occurrence. See, there is a difference!
Corrective action is easy in some ways because it is a reaction to a known problem. Preventive action is harder because there isn’t a problem yet. Preventive action is hunting down the problems before they occur, before anyone notices. It isn’t finding a method for catch out-of-tolerance errors during final inspection, it is a procedure for checking machine tolerances during production and catching them before they are out of spec.
Fixing existing problems is usually more urgent for companies, and is a good place to start; they are more obvious to find and analyze, and work well for getting familiar with root cause analysis. But ignoring the potential for improvements driven by preventive action, before there is a problem and an unhappy customer, keeps a company from having the highest quality it can achieve.
For more on using the system to improve your company, read Corrective Action vs Preventive Action.