Full Idea
If we imagine a possible world in which two clocks in a room make one clock from half the parts of each, the judgement 'these two actual clocks could have been a single clock' does not seem wholly false.
Gist of Idea
If we combined two clocks, it seems that two clocks may have become one clock.
Source
Graeme Forbes (The Metaphysics of Modality [1985], 7.4)
Book Reference
Forbes,Graeme: 'The Metaphysics of Modality' [OUP 1985], p.179
A Reaction
You would, of course, have sufficient parts left over to make a second clock, so they look like a destroyed clock, so I don't think I find Forbes's intuition on this one very persuasive.