Unlike primary reinforcers which are naturally reinforcing, secondary reinforcers are reinforcing only after the organism has been conditioned to find it reinforcing. Some stimulus that does not naturally provide reinforcement is paired with a primary reinforcer so that the organism begins to associate the secondary reinforcer with the primary reinforcer. For example. If you recall the Pavlov's dog case, the dog naturally salivated to the presence of meat powder. The meat powder serves as a primary reinforcer. But then pairing a sound with the meat powder over and over again, the sounds became reinforcing to the dog because it had been associated with the primary reinforcer (meat powder).