I've found the notion of a material object very puzzling. Here is something that would render it less puzzling to me:
- x is a material object if and only if x has limited location.
- There are locations and y has no location.
- There are no locations.
- There are locations and y is unlimited in location.
One might worry that there could be an animal that is as big as space itself, and then it would count as an immaterial object. But even though the animal would be everywhere, it wouldn't be everywhere in every part and respect. Its digestive system would be here but not there, and so on.
Alternately, one might stick to our definition of materiality as limited location, but modalize. Maybe "limited location" is a modal concept, so that a being that could be limited in location is thereby limited in location.