Life is full of interesting associations. Have we ever heard songs on the radio, or find ourselves in places, that instantly make we feel good because they have connected to special times we have had? When we smell freshly baked cookies, does it make our mouth water or stomach growl? These examples illustrate a learning process called classical conditioning, in which an organism learns to associate two stimuli (e. g., a song and a pleasant event), such that one stimulus (the song) comes to produce a response (feeling happy) that originally was produced only by the other stimulus (the pleasurable event).

Classical conditioning was the first type of learning to be discovered and studied within the behaviorist tradition. The major theorist in the development of classical conditioning is Ivan Pavlov. The original classical conditioning experiment comprised ringing a bell simultaneously with giving a meat powder to a dog. The meat powder or food was referred to as a natural innate or unconditioned stimulus (US), which evoked a natural or unconditioned response (UR), or unconditioned reflex in the form of salivation and served for satisfying hunger. UR does not require to be learned because it is already present in organism from their birth. Sound of the bell was referred to as a neutral external or condition stimulus (CS), which did not associate with any physiological function in the dog, and should be learned.

Pavlov called such types of stimuli "artificial stimuli". CS evokes a conditioned response (CR) or conditioned reflex. The purpose of the experiment was to motivate or condition the dog to react to the bell in the same way as it reacted to meat powder only. Pavlov did show, that if the bell (CS) was simultaneously presented with the meat powder (US) for a number of times, then the CS would certainly lead to the CR, which was originally initiated by food only. Therefore over time of learning the new condition the dog would be able to salivate in response to only the CS. Classical conditioning can help to explain the simple things in life such as a person's reaction to particular song, or smell as well as larger emotional problems such as fear and anxiety.

There is a prime example of classical conditioning in the lives of many adolescents. For a period of time whenever the phone rings and the daughter answers, she hears her boyfriends voice. At the sound of his voice, her heart begin thump. After while, whenever the phone rings her heart begins to thump. The CS in the phone ringing, the UCS is the boyfriend's voice, and the CR is her heart thumping.

The first time my friend took me to Don Pablos restaurant, I was in a bad mood and was not hungry as all. The movement I set foot inside the door, the wonderful smells coming from the kitchen caused my mouth to water. Now, whenever I pass by Don Pablos, whether I am hungry or not, my mouth begins to water. The CS is the restaurant itself. The UCS would be the smells coming from the kitchen. The CR would be my mouth watering.

Who have pets, those know, that as ever they begin to open a can with a pet's food, their pets are just running up against them for getting some food, because the pets associate getting food with the sound of the opener. If somebody touched a hot stove and got a burn, the he or she would never do that again, because touching the hot stove was associated with pain. The application of classical conditioning may be viewed in emotions, for example, association of fears, phobias in people with terrifying events or situations. If some music was associated with some strong terrible event, then hearing the same music, even in other place, would elicit memorials about that event.