Full Idea
A property ...is something which is strictly identical, strictly the same, in all its different instances.
Gist of Idea
All instances of some property are strictly identical
Source
David M. Armstrong (What is a Law of Nature? [1983], 06.2)
Book Reference
Armstrong,D.M.: 'What is a Law of Nature?' [CUP 1985], p.83
A Reaction
Some is gravitation one property, or an infinity of properties, for each of its values? What is the same between objects of different mass. I sort of believe in all the masses, but I'm not sure what 'mass' is. Abstraction, say I.