 One way to make the distinction between objects and properties is to look to expressions that refer to them. In first-order logic, there are (among other things) subjects and predicates. And predicates are predicated of subjects. Following Aristotle’s remarks on substance (Categories 1a20–4b19; see also the section on  category theory in the entry on Aristotle  and the entry on  classical logic),  Russell (1911) thought that these logical/linguistic reasons were the most persuasive reasons for positing an object/property distinction. He says: