In order to carry out classical conditioning, a neutral stimulus must be paired with an unconditioned stimulus, such as a loud noise.
By combining the neutral stimulus with the unconditioned one, a person or animal may be made to associate the two stimuli subconsciously. This is also observed in children that are taught to fear an object or an animal, where a neutral stimulus such as a cat may be paired with an unconditioned stimulus, such as the pain of being scratched.
