Discussion Groups / English Usage / March 2008

Up to a point. With scissors and knickers the emphasis is clearly on
the pair and not on the individual scissor or knicker, so the verb
would normally be singular. In general, though, we usually think of
people as individuals, so for me at least a plural verb would be more
natural (though I seem to recall that matters are ordered differently
on the other side of the Atlantic).

I'd only treat a pair of people as singular if they were twins, and
only then if the emphasis was on the twinniness, e.g, "Of all the pairs
of twins I've known there is only one that still lives around here".
Even then I'd be more likely to use a plural verb.