Deterrence-Severity vs certainty:
-> it was important to distinguish between the severity of punishment + the certainty of punishment
-> e.g. however severe the punishment might be for a particular offence, if theres a small chance of getting caught + convicted = it will be unlikely to deter many would-be offenders
-> e.g. theres a mandatory minimum sentence of 3 years imprisonment for committing a third domestic burglary, but only 5% of reported burglaries actually get a successful conviction, meaning that the likelihood of facing the punishment is very low
-> if the offender is very likely to get caught, then even a mild punishment could be an effective deterrent