Full Idea
A thing starts existing only once; and in the case of a clock its proper beginning was at about the time when its maker finished it.
Gist of Idea
A thing begins only once; for a clock, it is when its making is first completed
Source
David Wiggins (Sameness and Substance [1980], 3.3)
Book Reference
Wiggins,David: 'Sameness and Substance' [Blackwell 1980], p.91
A Reaction
I love the example that challenges this. Take the clock's parts and use them to make other clocks, then collect them up and reassemble the first clock. If the first clock has persisted through this, you have too many clocks. Wiggins spots some of this.