Full Idea
Universals and properties are different because a universal is supposed to be wholly present wherever it is instantiated. A property, by contrast, is spread around. The property of being a donkey is partly present wherever there is a donkey.
Gist of Idea
Universals are wholly present in their instances, whereas properties are spread around
Source
David Lewis (New work for a theory of universals [1983], 'Un and Prop')
Book Reference
'Properties', ed/tr. Mellor,D.H. /Oliver,A [OUP 1997], p.190
A Reaction
No mention of tropes. The claim that universals are widespread, and yet must be instantiated, is dealt with by Lewis's commitment to the existence of possible donkeys.