Full Idea
If whiteness were the thought as opposed to its object no two different men could think of it, and no one man could think of it twice. What many different thoughts of whiteness have in common is their object, and this object is different from all of them.
Gist of Idea
If we identify whiteness with a thought, we can never think of it twice; whiteness is the object of a thought
Source
Bertrand Russell (Problems of Philosophy [1912], Ch. 9)
Book Reference
Russell,Bertrand: 'The Problems of Philosophy' [OUP 1995], p.57
A Reaction
This seems to me a powerful argument in favour of thinking of universals as in some sense real - but in what sense? The crux is that Russell shows that we must find a place in our ontology for the content of thoughts, as well as of thoughts.