Third order conditioning is a psychological concept that demonstrates the potential for the formation of conditioned responses through a sequence of associative learning processes.

In first order conditioning, a neutral stimulus (NS) is repeatedly paired with an unconditioned stimulus (US) to elicit an unconditioned response (UR). Through this classical conditioning process, the neutral stimulus eventually becomes a conditioned stimulus (CS) that can elicit the same response, known as the conditioned response (CR).

In second order conditioning, a previously neutral stimulus (CS1) that has been associated with an unconditioned stimulus (US) through first order conditioning, is then paired with a new neutral stimulus (CS2) several times. Eventually, CS2 alone can elicit a conditioned response (CR) even without the presence of the original US.

In third order conditioning, the process is extended further. A new neutral stimulus (CS3) is introduced and repeatedly paired with CS2, which has acquired its conditioned properties through second order conditioning. As a result, CS3 itself becomes a conditioned stimulus (CS) capable of evoking a conditioned response (CR), even without the presence of CS2 or the original US.

Third order conditioning is an example of higher order conditioning, which demonstrates that classical conditioning can extend beyond a second order and suggests the potential for multiple levels of associative learning to influence behavioral responses.