What are the similarities and differences between Pavlov and Skinner?

Similarities: 

• Both psychologists focused on conditioning/modifying behavior


• Both forms of conditioning are forms of associative learning 

Pavlov: 

• Classical (respondent) conditioning 


• Focused on involuntary behaviors


• Placed signals before the reflex took place


• Animal learns association between uncontrollable events

Skinner: 

• Operant (instrumental) conditioning


• Focused on voluntary behaviors


• Aimed to reinforce or punish behaviors after they occurred 


• Animal learns the consequence to a certain behavior 

A Bit More In-Depth: 
 
The difference between the way classical conditioning and operant conditioning works is pretty simple once you understand the concepts behind each. 

(Pavlov) 

As mentioned above, classical conditioning focuses on involuntary behaviors.

For example, Pavlov's most notable experiment involving classical conditioning called for ringing a bell in order to cause dogs to salivate.
 
Prior to his experiment, Pavlov noticed that dogs salivated whenever they saw food which is an involuntary response on their part. To see if he could associate that involuntary response with a certain prompt, he added a bell as a neutral stimulus. 
 
For a period of time, he rang a bell whenever he fed the dogs and, eventually, they would salivate whenever they heard the bell, even if no food was present. 
 
Therefore, Pavlov was able to prove that an involuntary behavior could be associated with a certain stimulus.
 
(Skinner) 
 
Because operant conditioning focuses on voluntary behavior, Skinner's experiment was much different than Pavlov's. 
 
Skinner placed a rat in a box that contained a lever that would produce a food pellet when pushed. As the rat ran about the box, it accidentally bumped into the lever and it was provided with a pellet of food. The rat soon associated pushing the lever with receiving food (positive reinforcement) which increased the odds of it pushing the lever again. 
 
Skinner also noted that punishment could also modify the animal's behavior.

For example, if he were to take the food pellets out of his experiment, the rat would eventually stop pressing the lever after realizing it was no longer going to receive a reward for doing so. This is an example of negative punishment or "punishment by removal."
 
Unlike Pavlov's experiment with dogs, the behavior of the rats was completely voluntary and, due to instances of both positive and negative reinforcement, Skinner proved that they could learn to associate certain behaviors with certain consequences.