Mental States and Evidence: Inferring and Declaring the Mind

Mental states are an important part of criminal liability, and mens rea – the mental element of a given criminal offence – is widely regarded as a prerequisite thereof (setting aside, for the purposes of this discussion, strict liability offences). Many defences are premised on the accused not having the right mental state or having the “wrong” mental state, and liability and blame are often allotted with reference to mens rea. But how do we get to the point of saying, in law, that a given person D had a given mental state at the relevant time?