Severity vs. Certainty.If there is a sever punishment for a particular crime but the chances of being caught are low, this is unlikely to deter many offenders. (e.g. minimum sentence for third burglary is 3 years, only around 5% of reported burglaries result in conviction, so this is unlikely to be a deterrent). However, if an offender is likely to be caught even a smaller punishment can be an effective deterrent.Theory - right realism:1. Rational choice theory sees crime as a rational choice with criminals considering potential benefits and costs, therefore a high chance of getting caught will deter offending.2. Situational crime prevention strategies such as hardening make it harder to commit a successfully, therefore act as a deterrent.