How did Ivan Pavlov’s dog experiment demonstrate classical conditioning?

Ivan Pavlov’s experiments demonstrated classical conditioning by showing that an animal could learn to associate a neutral stimulus with a biological one, resulting in a new, predictable behavior.12

In his study, Pavlov observed that a hungry dog naturally salivated when presented with food, which he termed the unconditioned stimulus (US), and the resulting salivation was the unconditioned response (UR). Pavlov then introduced a neutral stimulus, such as the sound of a metronome or buzzer, immediately before providing the food.123

After repeated pairings, the dog began to salivate at the sound of the metronome alone, even before the food appeared. In this process:12
* The metronome became the conditioned stimulus (CS).12
* The salivation in response to the sound became the conditioned response (CR).12

This demonstrated that the dog had learned to associate the sound with the arrival of food, proving that behavior could be modified through systematic environmental reinforcement.12