Anchormen, chairs, dogs, flowers, and comets are things: If I have one anchorman and add another, I have two anchormen. My chair did not exist until it was assembled into that form. And if a comet hits Paraguay, it is no longer a comet.
Helium, gravy, wood, music, and joy are stuff: If some helium escapes my balloon, it seems wrong to say that I’ve lost a thing. If I divide my gravy into two portions, it’s still gravy. And if I chop my cabin into firewood, the amount of wood in the world does not seem to have changed.
We seem to distinguish between these two classes of existence. We can count things, but stuff forms a sort of cumulative mass. Things are made of stuff (crowns are made of gold), but stuff is made of things (gold is made of molecules). What’s at the bottom? And what leads us to make these distinctions?
(Kristie Miller, “Stuff,” American Philosophical Quarterly 46:1 [January 2009], 1-18.)