Classical conditioning is a learning theory discovered by Ivan Pavlov in 1927. Pavlov noticed that his dogs would salivate when they heard a bell, which he had previously associated with feeding time. He found that a neutral stimulus could become associated with an unconditioned stimulus through repeated pairing, resulting in a conditioned response. For example, a smoker trying to quit may associate smoking with driving, but chewing gum instead could become the new conditioned association. Classical conditioning demonstrates how stimuli and responses can be linked through learning.