Behavior chains seem pretty straightforward: it’s when an animal does a series of behaviors in a row, like links in a chain, ending in a reinforcer. Yet, behavior chains aren’t that simple! There is a tremendous lack of clarity in the training community about the definition of the term “chain.” I have researched the origins of the term and hope to clear up the confusion so we can better communicate with one another about chains and their many uses. 

Behavior chains

Before addressing the divergent definitions of a chain, let me provide an example of a typical chain: the retrieve. The retrieve is often referred to as a single behavior, but it is really a short sequence of separate behaviors that, when performed together in order, form a chain. When an animal is given a cue to retrieve something, the animal must (1) go to the object, (2) pick it up, (3) return to the trainer, (4) drop the object or place it in the trainer’s hand. These are four separate behaviors, linked together, giving the appearance of a single behavior.

Why is there confusion?

The source of confusion comes from the fact that in the field of Applied Behavior Analysis the term chain has a very specific meaning, while in the training community we use the term more loosely. For more than 100 years trainers have used the term “chain” to refer very broadly to a variety of types of behavior sequences, while in the behavior analysis community it has been used to identify a specific type of sequence. The example of the retrieve behavior would be considered a chain by both groups. The definitions have similarities, but there are also differences. In 1999, I suggested that we should refer to them as two different types of chains: technical and common (Ramirez, 1999).

Technical chains

A technical chain is what behavior analysts define as “a sequence of behaviors that occurs in a fixed order. Each behavior in the sequence serves as a discriminative stimulus (a cue) for the next response. Each behavior in the sequence (except the first behavior) also serves as a conditioned reinforcer that reinforces the previous response” (Kazdin, 2013). The trainer gives one cue and delivers reinforcement at the end of the chain. All other cues and reinforcers are built into the chain and are not delivered by the trainer.

Let’s look at the behavior of asking a dog to retrieve a ball. Behavior analysis looks at behavior in small units, so let’s break the sequence into A - antecedents (cues), B - behaviors, and C - consequences. A retrieval could be described like this:

   A1 – Trainer cues dog to bring ball

   B1 – Dog runs across field

   C1 – Opportunity to pick up ball reinforces running across field to ball

   A2 – Proximity to ball cues pick up the ball

   B2 – Dog picks up the ball

   C2 – Opportunity to run to trainer reinforces picking up ball

   A3 – Ball in mouth cues run back to trainer

   B3 – Dog runs back to trainer

   C3 – Opportunity to drop ball at trainer’s feet reinforces running back to trainer

   A4 – Proximity to trainer cues drop ball at trainer’s feet

   B4 – Dog drops ball at trainer’s feet

   C4 – Trainer marks and gives treat, or praise, or throws ball again

Combined, these units are a true “technical chain.” One cue from the trainer at the beginning and one reinforcer from the trainer at the end. All other cues and reinforcers are built into the chain. There is no way for the dog to bring the ball to the trainer successfully other than to do that sequence in that order.

Common chains

In a common chain, the trainer cues the animal at the beginning of the chain as well as at one or more points during the chain, delivers reinforcement at the end of the chain, and, at times, may deliver conditioned reinforcers throughout the chain.

Burch and Bailey in 1999 described a chain simply as “combining behaviors in a planned sequence.” In 2004, Karen Pryor referred to a chain as “a series of behaviors linked together in a continuous sequence by cues, delivered by the handler or from the environment, and maintained by a reinforcer at the end of the chain. Each cue serves as a marker and a reinforcer for the previous behavior, and the cue for the next behavior.” A typical agility sequence is an example: the dog is cued by the trainer throughout the sequence and no food or toy reinforcers are delivered until the completion of that sequence.

This type of “common chain” has been in the practical literature for more than 100 years and predates the scientific use of the term. I was able to find a reference to a chain in Frank C. Bostock’s 1903 book about the training of circus animals.

“In performance, Captain Jack Bonavita would command his lions to exhibit one trick after another, creating a long chain of tricks that dazzled the audience. No two performances were ever the same, each lion focused on getting to the end, when Captain Jack sent the lions back into their individual cages and rewarded them with a huge slab of raw steak. Only the most skilled of wild animal trainers could chain such a long series of tricks together in this manner.”

Untangling the confusion

Both technical and common chains are excellent ways to achieve a series of behaviors reliably. One technique is not better than the other—they are just different. The technical chain has a narrower definition than the common chain. Both are wonderful techniques to have in our toolbox. I still refer to common chains as chains when I speak with audiences who have used that term in the past, but I try to gently push them in the direction of the science. It’s not that the science is “better,” but I find value in us being able to speak the same language when we discuss a term, and the scientific version has the advantage of being peer-reviewed and subject to improvement over time.

The terminology challenge

We face conflicts between terms defined in the scientific literature and colloquial uses of the same word regularly. Few terms have caused as much confusion as the term “behavior chain.” Even scientists do not always agree on the exact definition. Remember that science is always evolving, and that definitions are simply convenient concept labels that help us create a common language that allows us to communicate and think more effectively.

As practical trainers, we develop techniques that work, but we are not always sure how to define them or what to call them. The science of behavior analysis examines these practical uses and does its best to define what we are doing. Together, we make the science and the practical applications of training better. We must learn from one another; ultimately that will help us improve the lives of the animals in our care.