Full Idea
When a piece of wood is divided in two halves, no new substance is generated. But there are now two substances, or the accidents of the two halves would be without a subject. They existed before hand, and were one piece of wood, but not in the same place.
Gist of Idea
Cut wood doesn't make a new substance, but seems to make separate subjects
Source
William of Ockham (Seven Quodlibets [1332], IV.19), quoted by Richard S. Westfall - Never at Rest: a biography of Isaac Newton 26.2
Book Reference
Pasnau,Robert: 'Metaphysical Themes 1274-1671' [OUP 2011], p.611
A Reaction
A nice example, demonstrating that there are substances within substances, contrary to the view of Duns Scotus. If a substance is just a subject for properties, it is hard to know what to make of this case.