 First, counterpart theory promises to explain the widespread elusiveness and context-dependence of essentialist judgements (Lewis 1983d, 42–3; Lewis 1986e, §4.5; cf. Kaplan 1979, 100–2). Could London have been located in Scotland? Could it have been founded in the 16th century? The answers aren’t obvious. For Lewis, this is not because we have imperfect access to London’s true essence, but simply because we have not settled exactly which other-worldly cities should qualify as counterparts of London. A London counterpart is a city that sufficiently resembles London, but the relevant resemblance criteria are often vague and context-dependent.