principles in formulating rules of crim law

• fair labelling 


  offence person is convicted of must accurately describe the crime committed

  need to be able to differentiate
• correspondence

  actus reus and mens rea don't correspond, liability must not exceed harm caused by mens rea

  e.g. mens rea for theft relates to actus reus
• maximum certainty 


  law must be as certain as possible. if elements aren't clear, isn't fair to convict
• no retrospective liability 


  where conduct is not an offence at the time committed, unfair to convict later.

  exception- world war crimes act 1991 meant could prosecute against acts in ww2