Behavioural interventions for reducing addiction are based on the assumption that addictive behaviours (e.g. smoking or gambling), are learnt and can be changed or modified by changing the consequences of the behaviour. Examples include aversion therapy and covert sensitisation, which are both based on the principles of classical conditioning. The difference is that aversion therapy involves creating a real unpleasant association, whereas covert sensitisation involves introducing an imagined unpleasant association.