Into to ABA 1: Why do we do the things we do?

Why do we do the things we do? : The three term contingency


In this post I am going to explain why people (all organsims) behave the way we do. That’s right, you can understand why people behave in the way they do, and it’s as simple as ABC. Trust me, It’s science.

Behaviours can be broken down into, what we call the three term contingency; Antecedent (A), Behaviour (B) and Consequence (C). When you analyse behaviours using this, you may have a deeper understanding of why people do the things they do. Behaviour doesn’t have to mystical and confusing when you understand the ABC of behaviours, thanks to Applied Behaviour Analysis (ABA).


Let’s break down the ABC so we understand which each means:

A) Antecedent: “A stimulus or environmental event”. Something occurs to the person in the environment or within their body. This includes a whole array of events, hunger/tiredness/thirst/etc., socialising, witnessing something happen, seeing , hearing, smelling, tasting something of interest, etc.. We will go through some more examples in a bit. In Applied Behaviour Analysis (ABA), assumptions about feelings of frustration, sadness, happiness or anger are avoided because we find these unhelpful in developing  an understanding behaviours.

B) Behaviour: “A measurable observable response”. A response that is observable, two or more people can see the behaviour occur and agree on what the behaviour was and how it looked, for example a spoken word/phrase, a jump, a laugh, a smile, etc..

C) Consequence: “A stimulus or environmental event”. Again, focus on the events in the environment, avoid assumptions about feelings and you can understand why behaviours occur. The consequence will either increase or decrease the number of times a behaviour will occur in the future under the circumstances outlined in the Antecedent. This will be done because something will be added or removed from their environment and this directly benefits the person.

“… the frequency with which a certain behaviour occurs depnds on what happens right after it occurs.that is, the behaviour’s immediate consequences.” Kearney (page 36)

What does all this mean? Let’s look at some examples:

ABC 1.1

This one is simple and straight forward. You get an itch on your arm, and you scratch it, then the itch goes away. In the future when you get an itch, you scratch it, because your behaviour resulting in the itch going away. This consequence relieves the itch and will result in an increase of this behaviour happening again in the future.

ABC 1.2

Imagine you’re driving home from work, you left late, traffic has been bad, and you’re thinking about going home and cooking dinner. You just want something easy and you want to veg out and relax! And then you see the fast food restaurant on your drive, and you pull into the drive through, order you food and voila! You have some food. Under these circumstances, of being hungry and seeing the fast food restaurant, you get your food. Under different circumstances, you’re hungry and you see a bus stop, if you pulled over and began to ask for a hamburger, you wouldn’t get one. The consequence would not lead to you pulling over to bus stops in the future, but going to the drive through has lead to the consequence you desire. So in the future, you will go to the fast food restaurant again. Make sense?

ABC 1.3

You see someone who says hello and you reply hey/hi/hello/etc., and the consequence is you have a good interaction and are socially acceptable. If you’re rude and don’t respond, people probably are going to talk to you again in the future. Unless it’s someone you don’t particularly like, the consequence of the pleasant interaction will lead to you responding to more greetings in the future.

ABC 1.4

You arrive at the train station and you were in a rush to get to the platform, and you arrive, expecting the traint o be there and it isn’t. There’s a few other people waiting, so may be you didn’t miss it? You ask someone near by “What time does the train arrive?” and they respond “1.35”. Now you know the time the train is coming, you are informed by the information and can make a decision about whether you wait, or quickly grab a coffee.

The purpose of this blog is to be a quick and simple introduction to the three term contingency so you can begin to understand behaviour. Behaviour is evoked because of events in the environment and it is the events in the environment that continue to reinforce behaviours so they continue to occur, or stop occurring.

“Consequences affect only future behaviour. Specifically, a behavioural consequence affects the relative frequency with which similar responses will be emitted in the future under similar stimulus conditions.” Cooper, Heron, & Heward (page 34).

Think about a behaviour that interests you and see if you can break it down into the ABC. Think about the child who cries at the supermarket until their parent gives them the sweet to keep them quiet so they can focus on completing their shop in peace, do you think the child will cry on the next visit to the supermarket, or the visit after that? I’d put money on it! What about the loud person at the party? They have a loud, sociable, bubbly personality, but they are merely a result of their environment. Being at the party, or seeing groups of people has been an antecedent for engaging in the behaviours that characterise their personality because the consequences have reinforced those behaviours. People have enjoyed their company, laughed at their jokes, listened to theirs stories and asked questions.

Taken from:

Behaviour is so easy to understand when you break it down into the ABC. So now you hold the key…


Check out for Part 2: why do we do the things we do?


Also, feel free to contact me about any questions or comments, by commenting below, emailing me at, using the contact form, or messaging me via Facebook or twitter.

<— Back to the Intro Series Homepage



Cooper, J. O., Heron, T. E., & Heward, W. L. (2007). Applied Behaviour Analysis (2nd ed.) New Jersey: Pearson Education, Inc

Kearney, A. J. (2008). Understanding Applied Behavior Analysis. Philadelphia, PA: Jessica Kingsley Publishers.

Further Reading/Listening:

Lynch Barbera, M. (2007). The Verbal Behavior Approach: How to teach children with Autism and Related Disorders (Chapter 2). Philadelphia, PA: Jessica Kingsley Publishers.

BehaviorBabe. (2013, June, 5). ABC’s of ABA. Retrieved from:



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