  It is worth concluding this section by returning to two questions distinguished at its outset: (i) should criminal responsibility require mens rea? (ii) what mens rea should it require? Question (i) is often discussed under the heading of strict liability. The literature distinguishes between various senses in which liability can be strict (Duff 2005; Gardner 2005, 68–69; Simester 2005, 22–23). Criminal liability for \(\phi\)ing is substantively strict if we can \(\phi\) without being culpable for \(\phi\)ing. It is formally strict if \(\phi\)ing lacks elements of mens rea. This second category can itself be subdivided. Liability is formally strict in the strong sense when there is no mens rea element at all. Liability is formally strict in the weak sense when at least one actus reus element has no corresponding element of mens rea. If (C) is a sound principle, criminal liability should not be substantively strict. If (MR) is sound, there should be no criminal liability that is formally strict in the strong sense. If the correspondence principle is sound, liability that is formally strict in the weak sense also should not exist.