Reinforcement describes how controlling particular Contingencies may affect the repetition of particular behaviours - what is confusing is that BOTH Positive and Negative Reinforcement encourage a behaviour.

Positive Reinforcement is where the contingency (i.e. the response to a behaviour) is pleasant.

A simple example of this is one of the effects of drugs, which is of inducing euphoria.

Negative Reinforcement, is where an unpleasant experience is removed as a result of the behaviour.

Staying with the same example as above, drugs may also remove pain, anxiety, and the unpleasant symptims of withdrawal. This is a powerful Reinforcement of the drug habit, although the "reward" is the removal of something unpleasant, rather than the delivery of something pleasant.

Using this:

The KeyWorker can use ABC Diary-keeping to analyze what might be the Reinforcers that are supporting a particular behaviour, and use this knowledge to plan simple behavioural interventions, which involve changing the Reinforcers, so that different Contingencies exist.

For example: Anton has rages, when he is destructive and abusive. After this he becomes tearful, and he receives comfort and support from his mother who hugs him. If the hugs act as a Positive Reinforcement, then a change would be to ensure that anton's mother gives hugs when he is behaving well (not in a rage) and that she expresses her sympathy and a wish to be helpful without lengthy hugs directy after a rage...