Full Idea
Objects are similar by virtue of possessing similar properties; properties, in contrast, are not similar in virtue of anything.
Gist of Idea
Similar objects have similar properties; properties are directly similar
Source
John Heil (From an Ontological Point of View [2003], 14.2)
Book Reference
Heil,John: 'From an Ontological Point of View' [OUP 2005], p.152
A Reaction
I am not sure if I can understand the concept of similarity if there is no answer to the question 'In what respect?' I suppose David Hume is happy to take resemblance as given and basic, but it could be defined as 'sharing identical properties'.