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Classical and instrumental conditioning are both models in psychology that attempt to explain behavior.
Classical conditioning, sometimes called Pavlovian conditioning, is the process of associating a neutral stimulus with some other stimulus that evokes a response. The goal is to get the neutral stimulus to evoke the same response. For example, a dog may begin to salivate when he sees his master because the dog knows this is the person who feeds him. The smell and taste of meat are unconditioned responses, meaning they prompt the dog to salivate naturally. Pavlov thought if he could associate a neutral stimulus (such as the sight of a certain person or the ringing of a bell) with the appearance/smell of the food, eventually the neutral stimulus (bell) could evoke the reaction (salivation) by itself.
Instrumental (or operant) conditioning is similar to classical conditioning, but whereas classical conditioning only involves the effects of the environment on the subject, instrumental conditioning involves the effect of the subject on the environment as well as the effects of the environment on the subject. Instrumental conditioning was found to be more applicable to studying human behavior because human intelligence and will are more complex than other animal subjects.
In the classical model, behavior is predicted in terms of stimuli. In the instrumental (operant) model, behavior is predicted based on the associations of stimuli with positive or negative reinforcement. For example, a rat will learn by trial and error that pushing a lever will produce food. When the lever produces food at different times or with different rations, the rat will learn to adapt to this. This is different from classical conditioning where a subject is conditioned to respond to a stimuli. In instrumental conditioning, the subject (rat) figures out how to produce the food. The rat thinks the lever will eventually produce food and in that sense the lever is a kind of stimulus. But it is also the rat acting on the environment, choosing when (depending on what the rat learns from the frequency of the lever producing the food) to pull the lever. This is the main difference between classical and instrumental conditioning in that classical explains the effect of the environment on the subject. Instrumental (operant – subject as “operator”) also explains how and why the subject acts on the environment to produce a result.