 The most common objection to counterpart theory is probably that it gives rise to a deviant and counter-intuitive modal logic. Lewis (1968) gives translation rules from the language of quantified modal logic to an extensional first-order language. These translation rules invalidate the “necessity of identity” and the “necessity of distinctness”, as well as familiar principles of modal logic such □(A ∧ B) → □A. Conversely, they do validate controversial principles such as the Converse Barcan Formula and the “necessity of existence”. It has also been argued that the rules can’t be extended to a language with a well-behaved ‘actually’ operator.