It has happened to all of us. From a distance we see the back of someone's head; it looks familiar. Unsure, though, we move closer, trying to take a better look. They walk with a gait we know so well; we see their body with all its characteristic rhythms and tics. We catch a glimpse of their face: yes, it is them, that old lover we have not seen for years. The electricity is still there, the faint trembling, the ache in the pit of the stomach. And yet...is the shape quite right? And surely they never had that mole...? Or: we see a face across a room; is that old Johnnie? We stare, half-indiscreetly, half-covertly, caught between a desire to make contact and fear of the mistake. The eyes and the mouth are the same, the way he lifts his glass identical; and yet...
It is disconcerting to see these impostors - doubly disconcerting because they are so good. We were right to be wrong: they do look almost identical. Our confidence is shaken, not only in our ability to recognise - old age and fading memories alone would account for that loss - but also in the uniqueness of the people we have met.
When we see these simulacra, especially if we encounter more than one of them, we begin to realise that perhaps there are only a limited number of permutations of eyes and noses and chins, the results of a genetic Identikit. The details may differ, but then so have the details of their lives to this point; the underlying bone-structure, flesh cover, and colouring are in essence the same.
Physical repetition is worrying enough, but what if this circumscribed range of possibilities extended to the mental sphere too? The characters of friends, family and lovers - those wonderful qualities that seemed so unique and so uniquely given to us - they too may be closely matched by other look- and think-alikes. What then of our special relationships - special with respect to what? To an entire class of matching people?
Worse follows. When we spot these coincidences of form in other people, we concede readily that sometimes the resemblances are startling; but if for a moment a friend or colleague suggests a similar correspondence of a third party - an acquaintance, a stranger even - with ourselves, the defences go up. The suggestion is preposterous, the proponent is clearly a fool or a knave. We protest overmuch because what applied to our loved ones applies equally to us: that we might not be unique in outward form or even in what, or in who, we are.
We can truthfully deny these parallels because we better than anyone know our superficial details: no one else has seen us so often, gazed at us in the mirror so much. For the same reason we spot supposed likenesses between friends and passers-by: we know the one reasonably well, the other not at all; we are ready to note the points of contact, and are blind to the tinier clashes. In its most extreme form, this knowledge mismatch accounts for the Westerner's inability to tell some Chinamen apart: to do so, the language of their faces must first be learnt. In other words, whether we or our friends really are duplicated by others comes down to a question of degree. How similar does similar have to be to matter?