Operant or instrumental conditioning and classical or Pavlovian conditioning were once thought to depend on fundamentally different learning mechanisms. In the Pavlovian paradigm, reinforcement (the US) is given whether the subject makes a conditioned response (CR) or not, whereas in the operant paradigm reinforcement is contingent on the CR. However, as we noted earlier, the discovery of autoshaping raised serious doubts in many quarters about the claim that there are in fact two distinct learning processes in conditioning. Autoshaping is now the method of choice for teaching pigeons to peck keys and rats to press levers. An autoshaping protocol is identical to the protocol that Pavlov used to teach dogs to salivate in response to tones and other conditioned stimuli (CS). The only difference is that the dog subject is replaced with a pigeon or a rat, the tone CS is replaced with key illumination or lever extension, and the CR that emerges as a consequence of the subject’s exposure to the contingency between the CS and reinforcement is key pecking or lever pressing. Just as dogs salivate to stimuli that predict food, so pigeons peck at a bright round stimulus that predicts grain and rats attempt to manipulate a lever whose extension predicts food. These are unconditioned responses to acquired knowledge. The pigeon and the rat have not learned to peck the key or press the lever, they have learned that the illuminated key or moving lever predicts food. The behavior that we observe is elicited by the knowledge the subjects have acquired.